From ad0c68ca5d3c5c3696547b0873181f9ac8d11aeb Mon Sep 17 00:00:00 2001
From: Nick Evans <2616208+nickevansuk@users.noreply.github.com>
Date: Thu, 17 Aug 2023 16:20:19 +0100
Subject: [PATCH] feat: Idempotency support (#552)

---
 .../test/features/README.md                   |  4 +-
 .../implemented/accept-proposal-book-test.js  |  1 +
 .../customer-reject-proposal-test.js          |  3 ++
 .../not-accept-proposal-book-test.js          |  3 ++
 .../seller-reject-proposal-test.js            |  3 ++
 .../proposal-amendment-book-test.js           |  4 ++
 .../implemented/amend-c1-and-c2-test.js       |  1 +
 .../implemented/amend-c1-test.js              |  1 +
 .../implemented/amend-c2-test.js              |  1 +
 .../c2-with-different-details-test.js         |  1 +
 .../test/features/criteria-requirements.json  |  6 +--
 .../payment/free-opportunities/README.md      |  3 +-
 .../opportunity-free-idempotency-test.js      | 33 +++++++++++++++
 ...portunity-free-without-checkpoints-test.js | 29 +++++++------
 .../payment/non-free-opportunities/README.md  |  3 +-
 .../opportunity-paid-idempotency-test.js      | 36 ++++++++++++++++
 ...portunity-paid-without-checkpoints-test.js | 29 +++++++------
 ...culation-gross-without-checkpoints-test.js | 29 +++++++------
 .../test/features/tests-implemented.json      |  4 +-
 .../test/helpers/flow-stages/b.js             | 36 +++++++++++++++-
 .../helpers/flow-stages/flow-stage-recipes.js | 41 +++++++++++++++----
 .../test/helpers/flow-stages/p.js             | 23 ++++++++++-
 .../test/templates/b-req.js                   |  7 ++--
 .../test/templates/c1-req.js                  |  4 +-
 .../test/templates/c2-req.js                  |  4 +-
 .../test/templates/common.js                  | 12 +++---
 26 files changed, 251 insertions(+), 70 deletions(-)
 create mode 100644 packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-idempotency-test.js
 create mode 100644 packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-idempotency-test.js

diff --git a/packages/openactive-integration-tests/test/features/README.md b/packages/openactive-integration-tests/test/features/README.md
index f70c85f0ec..0f17792a14 100644
--- a/packages/openactive-integration-tests/test/features/README.md
+++ b/packages/openactive-integration-tests/test/features/README.md
@@ -47,8 +47,8 @@ The tests for these features cover all known edge cases, including both happy an
 | notifications | Change of logistics notifications ([change-of-logistics-notifications](./notifications/change-of-logistics-notifications/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#change-of-logistics-notifications) | Notifications for when an opportunity's name, location, or start/end date/time are updated  | [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x12 |
 | notifications | Customer notice notifications ([customer-notice-notifications](./notifications/customer-notice-notifications/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#customer-notice-notifications) | Text notifications broadcast to all registered attendees of an opportunity | [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x4 |
 | notifications | Opportunity attendance updates ([opportunity-attendance-updates](./notifications/opportunity-attendance-updates/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#opportunity-attendance-updates) | Allowing the broker to recieve updates for when an attendee attends an event | [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x8 |
-| payment | Free opportunities ([free-opportunities](./payment/free-opportunities/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#free-opportunities) | The most simple form of booking, for free opportunities. Does not check for leases. | [TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x10 |
-| payment | Opportunities with a non-zero price ([non-free-opportunities](./payment/non-free-opportunities/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#step-by-step-process-description) | The most simple form of booking with payment. Does not check for leases. | [TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x6, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x2 |
+| payment | Free opportunities ([free-opportunities](./payment/free-opportunities/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#free-opportunities) | The most simple form of booking, for free opportunities. Does not check for leases. | [TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x14 |
+| payment | Opportunities with a non-zero price ([non-free-opportunities](./payment/non-free-opportunities/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#step-by-step-process-description) | The most simple form of booking with payment. Does not check for leases. | [TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x9, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x3 |
 | payment | Payment reconciliation detail validation ([payment-reconciliation-detail-validation](./payment/payment-reconciliation-detail-validation/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#payment-reconciliation-detail-validation) | Booking with valid, invalid, and missing Payment details | [TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x12, [TestOpportunityBookableUsingPayment](https://openactive.io/test-interface#TestOpportunityBookableUsingPayment) x15, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x5 |
 | payment | prepayment optional ([prepayment-optional](./payment/prepayment-optional/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#booking-without-payment) | Support for booking with optional payment | [TestOpportunityBookableNonFreePrepaymentOptional](https://openactive.io/test-interface#TestOpportunityBookableNonFreePrepaymentOptional) x8 |
 | payment | prepayment required ([prepayment-required](./payment/prepayment-required/README.md)) | Optional<br>[View Spec](https://www.openactive.io/open-booking-api/EditorsDraft/#booking-without-payment) | Support for booking with required payment | [TestOpportunityBookableNonFreePrepaymentRequired](https://openactive.io/test-interface#TestOpportunityBookableNonFreePrepaymentRequired) x8 |
diff --git a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/accept-proposal-book-test.js b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/accept-proposal-book-test.js
index 87466f80a5..297ee52186 100644
--- a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/accept-proposal-book-test.js
+++ b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/accept-proposal-book-test.js
@@ -56,6 +56,7 @@ FeatureHelper.describeFeature(module, {
       opportunityFeedExtractResponses: c2.getStage('assertOpportunityCapacityAfterC2').getOutput().opportunityFeedExtractResponses,
       orderItems: fetchOpportunities.getOutput().orderItems,
     }),
+    paymentIdentifierIfPaid: FlowStageRecipes.createRandomPaymentIdentifierIfPaid(),
   });
 
   // ## Set up tests
diff --git a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/customer-reject-proposal-test.js b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/customer-reject-proposal-test.js
index 4f67f6508d..302ad6fb62 100644
--- a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/customer-reject-proposal-test.js
+++ b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/customer-reject-proposal-test.js
@@ -40,6 +40,7 @@ FeatureHelper.describeFeature(module, {
 },
 (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
   const { fetchOpportunities, c1, c2, defaultFlowStageParams } = FlowStageRecipes.initialiseSimpleC1C2Flow(orderItemCriteriaList, logger);
+  const paymentIdentifierIfPaid = FlowStageRecipes.createRandomPaymentIdentifierIfPaid();
   const p = new PFlowStage({
     ...defaultFlowStageParams,
     prerequisite: c2.getLastStage(),
@@ -48,6 +49,7 @@ FeatureHelper.describeFeature(module, {
       totalPaymentDue: c2.getStage('c2').getOutput().totalPaymentDue,
       prepayment: c2.getStage('c2').getOutput().prepayment,
     }),
+    paymentIdentifierIfPaid,
   });
   const [customerRejection, orderFeedUpdate] = OrderFeedUpdateFlowStageUtils.wrap({
     wrappedStageFn: prerequisite => (new CustomerRejectOrderProposalFlowStage({
@@ -73,6 +75,7 @@ FeatureHelper.describeFeature(module, {
         orderProposalVersion: orderFeedUpdate.getOutput().orderProposalVersion,
         positionOrderIntakeFormMap: c1.getStage('c1').getOutput().positionOrderIntakeFormMap,
       }),
+      paymentIdentifierIfPaid,
     },
   });
 
diff --git a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/not-accept-proposal-book-test.js b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/not-accept-proposal-book-test.js
index 283c13333a..3de1205417 100644
--- a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/not-accept-proposal-book-test.js
+++ b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/not-accept-proposal-book-test.js
@@ -34,6 +34,7 @@ FeatureHelper.describeFeature(module, {
 },
 (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
   const { fetchOpportunities, c1, c2, defaultFlowStageParams } = FlowStageRecipes.initialiseSimpleC1C2Flow(orderItemCriteriaList, logger);
+  const paymentIdentifierIfPaid = FlowStageRecipes.createRandomPaymentIdentifierIfPaid();
   const p = new PFlowStage({
     ...defaultFlowStageParams,
     prerequisite: c2.getLastStage(),
@@ -42,6 +43,7 @@ FeatureHelper.describeFeature(module, {
       totalPaymentDue: c2.getStage('c2').getOutput().totalPaymentDue,
       prepayment: c2.getStage('c2').getOutput().prepayment,
     }),
+    paymentIdentifierIfPaid,
   });
   const b = FlowStageRecipes.runs.book.simpleBAssertCapacity(p, defaultFlowStageParams, {
     isExpectedToSucceed: false,
@@ -55,6 +57,7 @@ FeatureHelper.describeFeature(module, {
         orderProposalVersion: p.getOutput().orderProposalVersion,
         positionOrderIntakeFormMap: c1.getStage('c1').getOutput().positionOrderIntakeFormMap,
       }),
+      paymentIdentifierIfPaid,
     },
   });
 
diff --git a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/seller-reject-proposal-test.js b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/seller-reject-proposal-test.js
index cef0033ea4..d4537692c2 100644
--- a/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/seller-reject-proposal-test.js
+++ b/packages/openactive-integration-tests/test/features/approval/minimal-proposal/implemented/seller-reject-proposal-test.js
@@ -40,6 +40,7 @@ FeatureHelper.describeFeature(module, {
 },
 (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
   const { fetchOpportunities, c1, c2, defaultFlowStageParams } = FlowStageRecipes.initialiseSimpleC1C2Flow(orderItemCriteriaList, logger);
+  const paymentIdentifierIfPaid = FlowStageRecipes.createRandomPaymentIdentifierIfPaid();
   const p = new PFlowStage({
     ...defaultFlowStageParams,
     prerequisite: c2.getLastStage(),
@@ -48,6 +49,7 @@ FeatureHelper.describeFeature(module, {
       totalPaymentDue: c2.getStage('c2').getOutput().totalPaymentDue,
       prepayment: c2.getStage('c2').getOutput().prepayment,
     }),
+    paymentIdentifierIfPaid,
   });
   const [simulateSellerRejection, orderFeedUpdate] = OrderFeedUpdateFlowStageUtils.wrap({
     wrappedStageFn: prerequisite => (new TestInterfaceActionFlowStage({
@@ -79,6 +81,7 @@ FeatureHelper.describeFeature(module, {
         orderProposalVersion: orderFeedUpdate.getOutput().orderProposalVersion,
         positionOrderIntakeFormMap: c1.getStage('c1').getOutput().positionOrderIntakeFormMap,
       }),
+      paymentIdentifierIfPaid,
     },
   });
 
diff --git a/packages/openactive-integration-tests/test/features/approval/proposal-amendment/implemented/proposal-amendment-book-test.js b/packages/openactive-integration-tests/test/features/approval/proposal-amendment/implemented/proposal-amendment-book-test.js
index ce7e688c49..1455ef1d4c 100644
--- a/packages/openactive-integration-tests/test/features/approval/proposal-amendment/implemented/proposal-amendment-book-test.js
+++ b/packages/openactive-integration-tests/test/features/approval/proposal-amendment/implemented/proposal-amendment-book-test.js
@@ -41,6 +41,7 @@ FeatureHelper.describeFeature(module, {
 (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
   // ## Initiate Flow Stages
   const { fetchOpportunities, c1, c2, defaultFlowStageParams } = FlowStageRecipes.initialiseSimpleC1C2Flow(orderItemCriteriaList, logger);
+  const paymentIdentifierIfPaid = FlowStageRecipes.createRandomPaymentIdentifierIfPaid();
   const p = new PFlowStage({
     ...defaultFlowStageParams,
     prerequisite: c2.getLastStage(),
@@ -49,6 +50,7 @@ FeatureHelper.describeFeature(module, {
       totalPaymentDue: c2.getStage('c2').getOutput().totalPaymentDue,
       prepayment: c2.getStage('c2').getOutput().prepayment,
     }),
+    paymentIdentifierIfPaid,
   });
   const [simulateSellerAmendment, sellerAmendmentOrderFeedUpdate] = OrderFeedUpdateFlowStageUtils.wrap({
     // FlowStage that is getting wrapped
@@ -102,6 +104,7 @@ FeatureHelper.describeFeature(module, {
         orderProposalVersion: p.getOutput().orderProposalVersion,
         prepayment: p.getOutput().prepayment,
       }),
+      paymentIdentifierIfPaid,
     },
   });
   // Using the new proposal version should fail
@@ -116,6 +119,7 @@ FeatureHelper.describeFeature(module, {
         orderProposalVersion: sellerAmendmentOrderFeedUpdate.getOutput().orderProposalVersion,
         prepayment: sellerAmendmentOrderFeedUpdate.getOutput().prepayment,
       }),
+      paymentIdentifierIfPaid,
     },
   });
 
diff --git a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-and-c2-test.js b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-and-c2-test.js
index 5b0d082d82..4a73d17e29 100644
--- a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-and-c2-test.js
+++ b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-and-c2-test.js
@@ -77,6 +77,7 @@ FeatureHelper.describeFeature(module, {
       orderItems: secondAttemptFetchOpportunities.getOutput().orderItems,
       opportunityFeedExtractResponses: secondAttemptC2.getStage('assertOpportunityCapacityAfterC2').getOutput().opportunityFeedExtractResponses,
     }),
+    paymentIdentifierIfPaid: FlowStageRecipes.createRandomPaymentIdentifierIfPaid(),
   });
 
   // # Set up Tests
diff --git a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-test.js b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-test.js
index d4614c3fec..ef77bc20cc 100644
--- a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-test.js
+++ b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c1-test.js
@@ -74,6 +74,7 @@ FeatureHelper.describeFeature(module, {
       orderItems: secondAttemptFetchOpportunities.getOutput().orderItems,
       opportunityFeedExtractResponses: secondAttemptC2.getStage('assertOpportunityCapacityAfterC2').getOutput().opportunityFeedExtractResponses,
     }),
+    paymentIdentifierIfPaid: FlowStageRecipes.createRandomPaymentIdentifierIfPaid(),
   });
 
   // # Set up Tests
diff --git a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c2-test.js b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c2-test.js
index 084754f002..87b88b6ccd 100644
--- a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c2-test.js
+++ b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/amend-c2-test.js
@@ -69,6 +69,7 @@ FeatureHelper.describeFeature(module, {
       orderItems: secondAttemptFetchOpportunities.getOutput().orderItems,
       opportunityFeedExtractResponses: secondAttemptC2.getStage('assertOpportunityCapacityAfterC2').getOutput().opportunityFeedExtractResponses,
     }),
+    paymentIdentifierIfPaid: FlowStageRecipes.createRandomPaymentIdentifierIfPaid(),
   });
 
   // # Set up Tests
diff --git a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/c2-with-different-details-test.js b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/c2-with-different-details-test.js
index 1923d3a73e..b9387e2829 100644
--- a/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/c2-with-different-details-test.js
+++ b/packages/openactive-integration-tests/test/features/core/amending-order-quote/implemented/c2-with-different-details-test.js
@@ -60,6 +60,7 @@ FeatureHelper.describeFeature(module, {
       orderItems: secondAttemptFetchOpportunities.getOutput().orderItems,
       opportunityFeedExtractResponses: secondAttemptC2.getStage('assertOpportunityCapacityAfterC2').getOutput().opportunityFeedExtractResponses,
     }),
+    paymentIdentifierIfPaid: FlowStageRecipes.createRandomPaymentIdentifierIfPaid(),
   });
 
   // # Set up Tests
diff --git a/packages/openactive-integration-tests/test/features/criteria-requirements.json b/packages/openactive-integration-tests/test/features/criteria-requirements.json
index db704d5d7b..dbd7fb0534 100644
--- a/packages/openactive-integration-tests/test/features/criteria-requirements.json
+++ b/packages/openactive-integration-tests/test/features/criteria-requirements.json
@@ -194,13 +194,13 @@
     },
     "free-opportunities": {
       "primary": {
-        "TestOpportunityBookableFree": 10
+        "TestOpportunityBookableFree": 14
       }
     },
     "non-free-opportunities": {
       "primary": {
-        "TestOpportunityBookableNonFree": 6,
-        "TestOpportunityBookable": 2
+        "TestOpportunityBookableNonFree": 9,
+        "TestOpportunityBookable": 3
       }
     },
     "payment-reconciliation-detail-validation": {
diff --git a/packages/openactive-integration-tests/test/features/payment/free-opportunities/README.md b/packages/openactive-integration-tests/test/features/payment/free-opportunities/README.md
index 8ba9ed0c87..cd263923cd 100644
--- a/packages/openactive-integration-tests/test/features/payment/free-opportunities/README.md
+++ b/packages/openactive-integration-tests/test/features/payment/free-opportunities/README.md
@@ -12,7 +12,7 @@ See also: [.NET Tutorial](https://tutorials.openactive.io/open-booking-sdk/quick
 ### Test prerequisites
 Opportunities that match the following criteria must exist in the booking system (for each configured `bookableOpportunityTypesInScope`) for the configured primary Seller in order to use `useRandomOpportunities: true`. Alternatively the following `testOpportunityCriteria` values must be supported by the [test interface](https://openactive.io/test-interface/) of the booking system for `useRandomOpportunities: false`.
 
-[TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x10
+[TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x14
 
 
 ### Running tests for only this feature
@@ -37,6 +37,7 @@ Update `default.json` within `packages/openactive-integration-tests/config/` as
 
 | Identifier | Name | Description | Prerequisites per Opportunity Type |
 |------------|------|-------------|---------------|
+| [opportunity-free-idempotency](./implemented/opportunity-free-idempotency-test.js) | Successful booking of free opportunity with idempotency | Testing idempotency of the B call for free opportunities | [TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x4 |
 | [opportunity-free-must-not-include-prepayment](./implemented/opportunity-free-must-not-include-prepayment-test.js) | Free opportunities must have either a `openBookingPrepayment` value of Unspecified, or have no `openBookingPrepayment` specified | Assert that no opportunities that match criteria 'TestOpportunityBookableFreePrepaymentOptional' or 'TestOpportunityBookableFreePrepaymentRequired' are available in the opportunity feeds. |  |
 | [opportunity-free](./implemented/opportunity-free-test.js) | Successful booking without payment property | A successful end to end booking without the `payment` property included. | [TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x2 |
 | [opportunity-free-unnecessary-payment-error](./implemented/opportunity-free-unnecessary-payment-error-test.js) | Fail free bookings which include erroneous payment property | C1, C2 and B with payment property: payment property is provided but not expected in the request, so an UnnecessaryPaymentDetailsError must be returned. | [TestOpportunityBookableFree](https://openactive.io/test-interface#TestOpportunityBookableFree) x2 |
diff --git a/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-idempotency-test.js b/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-idempotency-test.js
new file mode 100644
index 0000000000..af2c9f1f7b
--- /dev/null
+++ b/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-idempotency-test.js
@@ -0,0 +1,33 @@
+const { omit } = require('lodash');
+const { FeatureHelper } = require('../../../../helpers/feature-helper');
+const { FlowStageRecipes, FlowStageUtils } = require('../../../../helpers/flow-stages');
+
+FeatureHelper.describeFeature(module, {
+  testCategory: 'payment',
+  testFeature: 'free-opportunities',
+  testFeatureImplemented: true,
+  testIdentifier: 'opportunity-free-idempotency',
+  testName: 'Successful booking of free opportunity with idempotency',
+  testDescription: 'Testing idempotency of the B call for free opportunities',
+  testOpportunityCriteria: 'TestOpportunityBookableFree',
+  // This must also be TestOpportunityBookableFree as the entire Order must be free.
+  controlOpportunityCriteria: 'TestOpportunityBookableFree',
+}, (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
+  const {
+    fetchOpportunities,
+    bookRecipe,
+    defaultFlowStageParams,
+    bookRecipeArgs,
+  } = FlowStageRecipes.initialiseSimpleC1C2BookFlow(orderItemCriteriaList, logger);
+  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(
+    orderItemCriteriaList,
+    bookRecipe,
+    defaultFlowStageParams,
+    omit(bookRecipeArgs, ['prerequisite']),
+  );
+  FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(fetchOpportunities);
+  FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(bookRecipe);
+  describe('idempotent repeat B', () => {
+    FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
+  });
+});
diff --git a/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-without-checkpoints-test.js b/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-without-checkpoints-test.js
index 0128e79922..85607dd2a3 100644
--- a/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-without-checkpoints-test.js
+++ b/packages/openactive-integration-tests/test/features/payment/free-opportunities/implemented/opportunity-free-without-checkpoints-test.js
@@ -1,3 +1,4 @@
+const { omit } = require('lodash');
 const { FeatureHelper } = require('../../../../helpers/feature-helper');
 const { FlowStageRecipes, FlowStageUtils } = require('../../../../helpers/flow-stages');
 
@@ -12,18 +13,22 @@ FeatureHelper.describeFeature(module, {
   testOpportunityCriteria: 'TestOpportunityBookableFree',
   // This must also be TestOpportunityBookableFree as the entire Order must be free.
   controlOpportunityCriteria: 'TestOpportunityBookableFree',
-}, (configuration, orderItemCriteriaList, featureIsImplemented, logger, opportunityType, bookingFlow) => {
-  const { fetchOpportunities, bookRecipe, defaultFlowStageParams, bookRecipeGetFirstStageInput, bookRecipeGetAssertOpportunityCapacityInput } = FlowStageRecipes.initialiseSimpleBookOnlyFlow(orderItemCriteriaList, logger);
-  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(orderItemCriteriaList, bookRecipe, defaultFlowStageParams, {
-    getFirstStageInput: bookRecipeGetFirstStageInput,
-    getAssertOpportunityCapacityInput: bookRecipeGetAssertOpportunityCapacityInput,
-  });
+}, (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
+  const {
+    fetchOpportunities,
+    bookRecipe,
+    defaultFlowStageParams,
+    bookRecipeArgs,
+  } = FlowStageRecipes.initialiseSimpleBookOnlyFlow(orderItemCriteriaList, logger);
+  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(
+    orderItemCriteriaList,
+    bookRecipe,
+    defaultFlowStageParams,
+    omit(bookRecipeArgs, ['prerequisite']),
+  );
   FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(fetchOpportunities);
   FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(bookRecipe);
-  // Remove this condition once https://github.com/openactive/OpenActive.Server.NET/issues/100 is fixed.
-  if (bookingFlow === 'OpenBookingApprovalFlow') {
-    describe('idempotent repeat B', () => {
-      FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
-    });
-  }
+  describe('idempotent repeat B', () => {
+    FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
+  });
 });
diff --git a/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/README.md b/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/README.md
index d8333661d5..82623512c3 100644
--- a/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/README.md
+++ b/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/README.md
@@ -12,7 +12,7 @@ See also: [.NET Tutorial](https://tutorials.openactive.io/open-booking-sdk/quick
 ### Test prerequisites
 Opportunities that match the following criteria must exist in the booking system (for each configured `bookableOpportunityTypesInScope`) for the configured primary Seller in order to use `useRandomOpportunities: true`. Alternatively the following `testOpportunityCriteria` values must be supported by the [test interface](https://openactive.io/test-interface/) of the booking system for `useRandomOpportunities: false`.
 
-[TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x6, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x2
+[TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x9, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x3
 
 
 ### Running tests for only this feature
@@ -37,6 +37,7 @@ Update `default.json` within `packages/openactive-integration-tests/config/` as
 
 | Identifier | Name | Description | Prerequisites per Opportunity Type |
 |------------|------|-------------|---------------|
+| [opportunity-paid-idempotency](./implemented/opportunity-paid-idempotency-test.js) | Successful booking of paid opportunity with idempotency | Testing idempotency of the B call for paid opportunities | [TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x3, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x1 |
 | [opportunity-paid](./implemented/opportunity-paid-test.js) | Successful booking with payment property | A successful end to end booking of a non-free opportunity with the `payment` property included if required. | [TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x3, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x1 |
 | [opportunity-paid-without-checkpoints](./implemented/opportunity-paid-without-checkpoints-test.js) | Successful booking without Checkpoints | Paid Opportunities should be bookable without using Checkpoints C1 & C2 if 1). tax calculations are not performed by the Booking System and 2). they do not require additional details | [TestOpportunityBookableNonFree](https://openactive.io/test-interface#TestOpportunityBookableNonFree) x3, [TestOpportunityBookable](https://openactive.io/test-interface#TestOpportunityBookable) x1 |
 
diff --git a/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-idempotency-test.js b/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-idempotency-test.js
new file mode 100644
index 0000000000..b764589220
--- /dev/null
+++ b/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-idempotency-test.js
@@ -0,0 +1,36 @@
+const { omit } = require('lodash');
+const { FeatureHelper } = require('../../../../helpers/feature-helper');
+const { FlowStageRecipes, FlowStageUtils } = require('../../../../helpers/flow-stages');
+
+FeatureHelper.describeFeature(module, {
+  testCategory: 'payment',
+  testFeature: 'non-free-opportunities',
+  testFeatureImplemented: true,
+  testIdentifier: 'opportunity-paid-idempotency',
+  testName: 'Successful booking of paid opportunity with idempotency',
+  testDescription: 'Testing idempotency of the B call for paid opportunities',
+  testOpportunityCriteria: 'TestOpportunityBookableNonFree',
+  controlOpportunityCriteria: 'TestOpportunityBookable',
+},
+(configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
+  // Initiate Flow Stages
+  const {
+    fetchOpportunities,
+    bookRecipe,
+    defaultFlowStageParams,
+    bookRecipeArgs,
+  } = FlowStageRecipes.initialiseSimpleC1C2BookFlow(orderItemCriteriaList, logger);
+  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(
+    orderItemCriteriaList,
+    bookRecipe,
+    defaultFlowStageParams,
+    omit(bookRecipeArgs, ['prerequisite']),
+  );
+
+  // Set up tests
+  FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(fetchOpportunities);
+  FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(bookRecipe);
+  describe('idempotent repeat B', () => {
+    FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
+  });
+});
diff --git a/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-without-checkpoints-test.js b/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-without-checkpoints-test.js
index 98637eaf35..cc7f063461 100644
--- a/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-without-checkpoints-test.js
+++ b/packages/openactive-integration-tests/test/features/payment/non-free-opportunities/implemented/opportunity-paid-without-checkpoints-test.js
@@ -1,3 +1,4 @@
+const { omit } = require('lodash');
 const { FeatureHelper } = require('../../../../helpers/feature-helper');
 const { FlowStageRecipes, FlowStageUtils } = require('../../../../helpers/flow-stages');
 
@@ -19,21 +20,25 @@ FeatureHelper.describeFeature(module, {
   runOnlyIf: !IMPLEMENTED_FEATURES['business-to-consumer-tax-calculation-gross']
     && !IMPLEMENTED_FEATURES['business-to-consumer-tax-calculation-net'],
 },
-(configuration, orderItemCriteriaList, featureIsImplemented, logger, opportunityType, bookingFlow) => {
+(configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
   // Initiate Flow Stages
-  const { fetchOpportunities, bookRecipe, defaultFlowStageParams, bookRecipeGetFirstStageInput, bookRecipeGetAssertOpportunityCapacityInput } = FlowStageRecipes.initialiseSimpleBookOnlyFlow(orderItemCriteriaList, logger);
-  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(orderItemCriteriaList, bookRecipe, defaultFlowStageParams, {
-    getFirstStageInput: bookRecipeGetFirstStageInput,
-    getAssertOpportunityCapacityInput: bookRecipeGetAssertOpportunityCapacityInput,
-  });
+  const {
+    fetchOpportunities,
+    bookRecipe,
+    defaultFlowStageParams,
+    bookRecipeArgs,
+  } = FlowStageRecipes.initialiseSimpleBookOnlyFlow(orderItemCriteriaList, logger);
+  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(
+    orderItemCriteriaList,
+    bookRecipe,
+    defaultFlowStageParams,
+    omit(bookRecipeArgs, ['prerequisite']),
+  );
 
   // Set up tests
   FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(fetchOpportunities);
   FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(bookRecipe);
-  // Remove this condition once https://github.com/openactive/OpenActive.Server.NET/issues/100 is fixed.
-  if (bookingFlow === 'OpenBookingApprovalFlow') {
-    describe('idempotent repeat B', () => {
-      FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
-    });
-  }
+  describe('idempotent repeat B', () => {
+    FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
+  });
 });
diff --git a/packages/openactive-integration-tests/test/features/tax/business-to-consumer-tax-calculation-gross/implemented/business-to-consumer-tax-calculation-gross-without-checkpoints-test.js b/packages/openactive-integration-tests/test/features/tax/business-to-consumer-tax-calculation-gross/implemented/business-to-consumer-tax-calculation-gross-without-checkpoints-test.js
index 1b17f439de..a88ba4b7b2 100644
--- a/packages/openactive-integration-tests/test/features/tax/business-to-consumer-tax-calculation-gross/implemented/business-to-consumer-tax-calculation-gross-without-checkpoints-test.js
+++ b/packages/openactive-integration-tests/test/features/tax/business-to-consumer-tax-calculation-gross/implemented/business-to-consumer-tax-calculation-gross-without-checkpoints-test.js
@@ -1,3 +1,4 @@
+const { omit } = require('lodash');
 const { FeatureHelper } = require('../../../../helpers/feature-helper');
 const { FlowStageRecipes, FlowStageUtils } = require('../../../../helpers/flow-stages');
 
@@ -13,18 +14,22 @@ FeatureHelper.describeFeature(module, {
   testOpportunityCriteria: 'TestOpportunityBookableNonFreeTaxGross',
   // the simple tests can only work if all OrderItems have the same tax mode
   controlOpportunityCriteria: 'TestOpportunityBookableNonFreeTaxGross',
-}, (configuration, orderItemCriteriaList, featureIsImplemented, logger, opportunityType, bookingFlow) => {
-  const { fetchOpportunities, bookRecipe, defaultFlowStageParams, bookRecipeGetFirstStageInput, bookRecipeGetAssertOpportunityCapacityInput } = FlowStageRecipes.initialiseSimpleBookOnlyFlow(orderItemCriteriaList, logger);
-  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(orderItemCriteriaList, bookRecipe, defaultFlowStageParams, {
-    getFirstStageInput: bookRecipeGetFirstStageInput,
-    getAssertOpportunityCapacityInput: bookRecipeGetAssertOpportunityCapacityInput,
-  });
+}, (configuration, orderItemCriteriaList, featureIsImplemented, logger) => {
+  const {
+    fetchOpportunities,
+    bookRecipe,
+    defaultFlowStageParams,
+    bookRecipeArgs,
+  } = FlowStageRecipes.initialiseSimpleBookOnlyFlow(orderItemCriteriaList, logger);
+  const idempotentRepeatB = FlowStageRecipes.idempotentRepeatBAfterBook(
+    orderItemCriteriaList,
+    bookRecipe,
+    defaultFlowStageParams,
+    omit(bookRecipeArgs, ['prerequisite']),
+  );
   FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(fetchOpportunities);
   FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(bookRecipe);
-  // Remove this condition once https://github.com/openactive/OpenActive.Server.NET/issues/100 is fixed.
-  if (bookingFlow === 'OpenBookingApprovalFlow') {
-    describe('idempotent repeat B', () => {
-      FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
-    });
-  }
+  describe('idempotent repeat B', () => {
+    FlowStageUtils.describeRunAndCheckIsSuccessfulAndValid(idempotentRepeatB);
+  });
 });
diff --git a/packages/openactive-integration-tests/test/features/tests-implemented.json b/packages/openactive-integration-tests/test/features/tests-implemented.json
index 30d40853d8..fb06a6be46 100644
--- a/packages/openactive-integration-tests/test/features/tests-implemented.json
+++ b/packages/openactive-integration-tests/test/features/tests-implemented.json
@@ -162,11 +162,11 @@
       "notImplementedTestFiles": 0
     },
     "free-opportunities": {
-      "implementedTestFiles": 5,
+      "implementedTestFiles": 6,
       "notImplementedTestFiles": 1
     },
     "non-free-opportunities": {
-      "implementedTestFiles": 2,
+      "implementedTestFiles": 3,
       "notImplementedTestFiles": 1
     },
     "payment-reconciliation-detail-validation": {
diff --git a/packages/openactive-integration-tests/test/helpers/flow-stages/b.js b/packages/openactive-integration-tests/test/helpers/flow-stages/b.js
index 5242867723..d7c8ba2c20 100644
--- a/packages/openactive-integration-tests/test/helpers/flow-stages/b.js
+++ b/packages/openactive-integration-tests/test/helpers/flow-stages/b.js
@@ -37,9 +37,24 @@ const { FlowStageUtils } = require('./flow-stage-utils');
  * @param {RequestHelperType} args.requestHelper
  * @param {string | null} args.brokerRole
  * @param {PositionOrderIntakeFormMap} args.positionOrderIntakeFormMap
+ * @param {string} args.paymentIdentifierIfPaid
  * @returns {Promise<Output>}
  */
-async function runB({ templateRef, accessPass, brokerRole, uuid, sellerConfig, customer, orderItems, totalPaymentDue, prepayment, orderProposalVersion, requestHelper, positionOrderIntakeFormMap }) {
+async function runB({
+  templateRef,
+  accessPass,
+  brokerRole,
+  uuid,
+  sellerConfig,
+  customer,
+  orderItems,
+  totalPaymentDue,
+  prepayment,
+  orderProposalVersion,
+  requestHelper,
+  positionOrderIntakeFormMap,
+  paymentIdentifierIfPaid,
+}) {
   /** @type {BReqTemplateData} */
   const params = {
     orderType: 'Order',
@@ -52,6 +67,7 @@ async function runB({ templateRef, accessPass, brokerRole, uuid, sellerConfig, c
     brokerRole,
     positionOrderIntakeFormMap,
     customer,
+    paymentIdentifier: paymentIdentifierIfPaid,
   };
   const response = await requestHelper.putOrder(uuid, params, templateRef);
   const bookingSystemOrder = response.body;
@@ -81,8 +97,23 @@ class BFlowStage extends FlowStage {
    * @param {string} args.uuid
    * @param {SellerConfig} args.sellerConfig
    * @param {Customer} [args.customer]
+   * @param {string} args.paymentIdentifierIfPaid This Payment Identifier will be used if this is a paid
+   *   booking. Otherwise, it won't be. This is specified as an arg to allow for consistency between idempotent
+   *   B calls.
    */
-  constructor({ templateRef, accessPass, brokerRole, prerequisite, getInput, logger, requestHelper, uuid, sellerConfig, customer }) {
+  constructor({
+    templateRef,
+    accessPass,
+    brokerRole,
+    prerequisite,
+    getInput,
+    logger,
+    requestHelper,
+    uuid,
+    sellerConfig,
+    customer,
+    paymentIdentifierIfPaid,
+  }) {
     super({
       prerequisite,
       getInput,
@@ -102,6 +133,7 @@ class BFlowStage extends FlowStage {
           orderProposalVersion,
           requestHelper,
           positionOrderIntakeFormMap,
+          paymentIdentifierIfPaid,
         });
       },
       itSuccessChecksFn: FlowStageUtils.simpleHttp201SuccessChecks(),
diff --git a/packages/openactive-integration-tests/test/helpers/flow-stages/flow-stage-recipes.js b/packages/openactive-integration-tests/test/helpers/flow-stages/flow-stage-recipes.js
index 335a4efc28..9dd6297dbb 100644
--- a/packages/openactive-integration-tests/test/helpers/flow-stages/flow-stage-recipes.js
+++ b/packages/openactive-integration-tests/test/helpers/flow-stages/flow-stage-recipes.js
@@ -1,3 +1,4 @@
+const shortid = require('shortid');
 const { AssertOpportunityCapacityFlowStage } = require('./assert-opportunity-capacity');
 const { BFlowStage } = require('./b');
 const { BookRecipe } = require('./book-recipe');
@@ -63,6 +64,9 @@ const { TestInterfaceActionFlowStage } = require('./test-interface-action');
  *   AssertOpportunityCapacity flow stage, which runs after the booking is complete
  * @property {GetOpportunityExpectedCapacity} [getOpportunityExpectedCapacity] If not provided, this will
  *   default to using getOpportunityExpectedCapacityAfterBook(..)
+ * @property {string} paymentIdentifierIfPaid This Payment Identifier will be used if this is a paid
+   *   booking. Otherwise, it won't be. This is specified as an arg to allow for consistency between idempotent
+   *   B/P calls.
  */
 
 const RUN_TESTS_WHICH_FAIL_REFIMPL = process.env.RUN_TESTS_WHICH_FAIL_REFIMPL === 'true';
@@ -103,7 +107,8 @@ const FlowStageRecipes = {
         brokerRole,
       },
     );
-    const bookRecipe = FlowStageRecipes.book(orderItemCriteriaList, defaultFlowStageParams, {
+    /** @type {BookRecipeArgs} */
+    const bookRecipeArgs = {
       prerequisite: c2.getLastStage(),
       accessPass,
       brokerRole,
@@ -119,7 +124,9 @@ const FlowStageRecipes = {
         orderItems: fetchOpportunities.getOutput().orderItems,
       }),
       isExpectedToFail: bookExpectToFail,
-    });
+      paymentIdentifierIfPaid: FlowStageRecipes.createRandomPaymentIdentifierIfPaid(),
+    };
+    const bookRecipe = FlowStageRecipes.book(orderItemCriteriaList, defaultFlowStageParams, bookRecipeArgs);
 
     return {
       fetchOpportunities,
@@ -129,6 +136,7 @@ const FlowStageRecipes = {
       // This is included in the result so that additional stages can be added using
       // these params.
       defaultFlowStageParams,
+      bookRecipeArgs,
     };
   },
   /**
@@ -286,13 +294,20 @@ const FlowStageRecipes = {
       opportunityFeedExtractResponses: fetchOpportunities.getOutput().opportunityFeedExtractResponses,
       orderItems: fetchOpportunities.getOutput().orderItems,
     });
-    const bookRecipe = FlowStageRecipes.book(orderItemCriteriaList, defaultFlowStageParams, {
+    const bookRecipeGetOpportunityExpectedCapacity = AssertOpportunityCapacityFlowStage.getOpportunityExpectedCapacityAfterBookOnly(
+      isExpectedToSucceed,
+    );
+    const bookRecipePaymentIdentifierIfPaid = FlowStageRecipes.createRandomPaymentIdentifierIfPaid();
+    /** @type {BookRecipeArgs} */
+    const bookRecipeArgs = {
       prerequisite: fetchOpportunities,
       isExpectedToFail: !isExpectedToSucceed,
       getFirstStageInput: bookRecipeGetFirstStageInput,
       getAssertOpportunityCapacityInput: bookRecipeGetAssertOpportunityCapacityInput,
-      getOpportunityExpectedCapacity: AssertOpportunityCapacityFlowStage.getOpportunityExpectedCapacityAfterBookOnly(isExpectedToSucceed),
-    });
+      getOpportunityExpectedCapacity: bookRecipeGetOpportunityExpectedCapacity,
+      paymentIdentifierIfPaid: bookRecipePaymentIdentifierIfPaid,
+    };
+    const bookRecipe = FlowStageRecipes.book(orderItemCriteriaList, defaultFlowStageParams, bookRecipeArgs);
     return {
       fetchOpportunities,
       bookRecipe,
@@ -300,8 +315,7 @@ const FlowStageRecipes = {
       // these params.
       defaultFlowStageParams,
       // These can be used to create an idempotent second B stage.
-      bookRecipeGetFirstStageInput,
-      bookRecipeGetAssertOpportunityCapacityInput,
+      bookRecipeArgs,
     };
   },
   /**
@@ -367,6 +381,7 @@ const FlowStageRecipes = {
         bookRecipeGetFirstStageInput: bookRecipeArgs.getFirstStageInput,
         defaultFlowStageParams,
         prerequisite: bookRecipe.lastStage,
+        paymentIdentifierIfPaid: bookRecipeArgs.paymentIdentifierIfPaid,
       });
     }
     const bookRecipeArgsWithPrerequisite = { ...bookRecipeArgs, prerequisite: bookRecipe.lastStage };
@@ -423,6 +438,7 @@ const FlowStageRecipes = {
     getFirstStageInput,
     getAssertOpportunityCapacityInput,
     isExpectedToFail = null,
+    paymentIdentifierIfPaid,
     ...args
   }) {
     const b = new BFlowStage({
@@ -432,6 +448,7 @@ const FlowStageRecipes = {
       brokerRole,
       accessPass,
       getInput: getFirstStageInput,
+      paymentIdentifierIfPaid,
     });
     const getOpportunityExpectedCapacity = args.getOpportunityExpectedCapacity
       ?? AssertOpportunityCapacityFlowStage.getOpportunityExpectedCapacityAfterBook(!(isExpectedToFail ?? false));
@@ -467,6 +484,7 @@ const FlowStageRecipes = {
     getFirstStageInput,
     getAssertOpportunityCapacityInput,
     isExpectedToFail = null,
+    paymentIdentifierIfPaid,
     ...args
   }) {
     const p = new PFlowStage({
@@ -476,6 +494,7 @@ const FlowStageRecipes = {
       brokerRole,
       accessPass,
       getInput: getFirstStageInput,
+      paymentIdentifierIfPaid,
     });
     const [simulateSellerApproval, orderFeedUpdateCollector] = OrderFeedUpdateFlowStageUtils.wrap({
       wrappedStageFn: orderFeedUpdateListener => (new TestInterfaceActionFlowStage({
@@ -503,6 +522,7 @@ const FlowStageRecipes = {
         defaultFlowStageParams,
         prerequisite: orderFeedUpdateListener,
         bookRecipeGetFirstStageInput: getFirstStageInput,
+        paymentIdentifierIfPaid,
       }),
       orderFeedUpdateParams: {
         ...defaultFlowStageParams,
@@ -766,6 +786,9 @@ const FlowStageRecipes = {
       },
     },
   },
+  createRandomPaymentIdentifierIfPaid() {
+    return shortid.generate();
+  },
 };
 
 /**
@@ -776,8 +799,9 @@ const FlowStageRecipes = {
  * @param {DefaultFlowStageParams} args.defaultFlowStageParams
  * @param {UnknownFlowStageType} args.prerequisite
  * @param {() => import('./p').Input} args.bookRecipeGetFirstStageInput
+ * @param {string} args.paymentIdentifierIfPaid
  */
-function bAfterP({ p, defaultFlowStageParams, prerequisite, bookRecipeGetFirstStageInput }) {
+function bAfterP({ p, defaultFlowStageParams, prerequisite, bookRecipeGetFirstStageInput, paymentIdentifierIfPaid }) {
   return new BFlowStage({
     ...defaultFlowStageParams,
     prerequisite,
@@ -793,6 +817,7 @@ function bAfterP({ p, defaultFlowStageParams, prerequisite, bookRecipeGetFirstSt
         prepayment: p.getOutput().prepayment,
       };
     },
+    paymentIdentifierIfPaid,
   });
 }
 
diff --git a/packages/openactive-integration-tests/test/helpers/flow-stages/p.js b/packages/openactive-integration-tests/test/helpers/flow-stages/p.js
index 46222a157a..c933a0c30f 100644
--- a/packages/openactive-integration-tests/test/helpers/flow-stages/p.js
+++ b/packages/openactive-integration-tests/test/helpers/flow-stages/p.js
@@ -36,6 +36,7 @@ const { FlowStageUtils } = require('./flow-stage-utils');
  * @param {PositionOrderIntakeFormMap} args.positionOrderIntakeFormMap
  * @param {AccessPassItem[] | null} [args.accessPass]
  * @param {string | null} args.brokerRole
+ * @param {string} args.paymentIdentifierIfPaid
  * @returns {Promise<Output>}
  */
 async function runP({
@@ -50,8 +51,9 @@ async function runP({
   accessPass,
   brokerRole,
   requestHelper,
+  paymentIdentifierIfPaid,
 }) {
-  /** @type {import('../../templates/b-req').BReqTemplateData} */
+  /** @type {import('../../templates/b-req').PReqTemplateData} */
   const params = {
     orderType: 'OrderProposal',
     sellerId: sellerConfig['@id'],
@@ -62,6 +64,7 @@ async function runP({
     brokerRole,
     positionOrderIntakeFormMap,
     customer,
+    paymentIdentifier: paymentIdentifierIfPaid,
   };
   const response = await requestHelper.putOrderProposal(uuid, params, templateRef);
   const bookingSystemOrder = response.body;
@@ -92,8 +95,23 @@ class PFlowStage extends FlowStage {
    * @param {string} args.uuid
    * @param {SellerConfig} args.sellerConfig
    * @param {Customer} [args.customer]
+   * @param {string} args.paymentIdentifierIfPaid This Payment Identifier will be used if this is a paid
+   *   booking. Otherwise, it won't be. This is specified as an arg to allow for consistency between idempotent
+   *   P calls.
    */
-  constructor({ templateRef, accessPass, brokerRole, prerequisite, getInput, logger, requestHelper, uuid, sellerConfig, customer }) {
+  constructor({
+    templateRef,
+    accessPass,
+    brokerRole,
+    prerequisite,
+    getInput,
+    logger,
+    requestHelper,
+    uuid,
+    sellerConfig,
+    customer,
+    paymentIdentifierIfPaid,
+  }) {
     super({
       prerequisite,
       getInput,
@@ -112,6 +130,7 @@ class PFlowStage extends FlowStage {
           prepayment,
           positionOrderIntakeFormMap,
           requestHelper,
+          paymentIdentifierIfPaid,
         });
       },
       itSuccessChecksFn: FlowStageUtils.simpleHttp201SuccessChecks(),
diff --git a/packages/openactive-integration-tests/test/templates/b-req.js b/packages/openactive-integration-tests/test/templates/b-req.js
index d067e501ae..60211e7682 100644
--- a/packages/openactive-integration-tests/test/templates/b-req.js
+++ b/packages/openactive-integration-tests/test/templates/b-req.js
@@ -43,6 +43,7 @@ const { createPaymentPart, isPaidOpportunity, isPaymentAvailable, addOrderItemIn
  *   brokerRole?: string | null,
  *   positionOrderIntakeFormMap: {[k:string]: import('../helpers/flow-stages/flow-stage').OrderItemIntakeForm},
  *   customer: import('../helpers/flow-stages/flow-stage-utils').Customer,
+ *   paymentIdentifier?: string
  * }} BReqTemplateData
  *
  * @typedef {Omit<BReqTemplateData, 'orderProposalVersion'>} PReqTemplateData P accepts the same sort of requests as B.
@@ -75,7 +76,7 @@ function createAfterPBReq(data) {
     orderProposalVersion: data.orderProposalVersion,
   };
   if (isPaymentAvailable(data)) {
-    result.payment = createPaymentPart();
+    result.payment = createPaymentPart(data.paymentIdentifier);
   }
   return result;
 }
@@ -199,7 +200,7 @@ function createPaidWithPaymentBReq(data) {
       price: data.totalPaymentDue,
       priceCurrency: 'GBP',
     },
-    payment: createPaymentPart(),
+    payment: createPaymentPart(data.paymentIdentifier),
   };
 }
 
@@ -221,7 +222,7 @@ function createStandardPaidBReq(data) {
   if (isPaymentAvailable(data)) {
     return {
       ...reqWithoutPayment,
-      payment: createPaymentPart(),
+      payment: createPaymentPart(data.paymentIdentifier),
     };
   }
   return reqWithoutPayment;
diff --git a/packages/openactive-integration-tests/test/templates/c1-req.js b/packages/openactive-integration-tests/test/templates/c1-req.js
index e2dc3f9329..aecfa6be77 100644
--- a/packages/openactive-integration-tests/test/templates/c1-req.js
+++ b/packages/openactive-integration-tests/test/templates/c1-req.js
@@ -56,7 +56,7 @@ function createStandardC1Req(data) {
       orderItemIntakeForm: undefined,
       orderItemIntakeFormResponse: undefined,
     })),
-    payment: createPaymentPart(false),
+    payment: createPaymentPart(),
   };
 }
 
@@ -150,7 +150,7 @@ function createIncorrectReconciliationDetails(data) {
   const req = createStandardC1Req(data);
   // Always include payment details, regardless of if payment reconciliation
   // details are available in the config, as per the spec for Payment reconciliation detail validation
-  if (!req.payment) req.payment = createPaymentPart(false, true);
+  if (!req.payment) req.payment = createPaymentPart(undefined, true);
   if (req.payment.accountId) {
     req.payment.accountId = `invalid-${shortid.generate()}`;
   }
diff --git a/packages/openactive-integration-tests/test/templates/c2-req.js b/packages/openactive-integration-tests/test/templates/c2-req.js
index ffb660b26f..6aef3df814 100644
--- a/packages/openactive-integration-tests/test/templates/c2-req.js
+++ b/packages/openactive-integration-tests/test/templates/c2-req.js
@@ -108,7 +108,7 @@ function createStandardC2Req(data) {
       orderItemIntakeForm: undefined,
       orderItemIntakeFormResponse: undefined,
     })),
-    payment: createPaymentPart(false),
+    payment: createPaymentPart(),
   };
 }
 
@@ -264,7 +264,7 @@ function createIncorrectReconciliationDetails(data) {
   const req = createStandardC2Req(data);
   // Always include payment details, regardless of if payment reconciliation
   // details are available in the config, as per the spec for Payment reconciliation detail validation
-  if (!req.payment) req.payment = createPaymentPart(false, true);
+  if (!req.payment) req.payment = createPaymentPart(undefined, true);
   if (req.payment.accountId) {
     req.payment.accountId = `invalid-${shortid.generate()}`;
   }
diff --git a/packages/openactive-integration-tests/test/templates/common.js b/packages/openactive-integration-tests/test/templates/common.js
index a6598f4b5a..133a9d2034 100644
--- a/packages/openactive-integration-tests/test/templates/common.js
+++ b/packages/openactive-integration-tests/test/templates/common.js
@@ -1,5 +1,4 @@
 const { isNil } = require('lodash');
-const shortid = require('shortid');
 
 /**
  * @typedef {import('../helpers/flow-stages/fetch-opportunities').OrderItem} OrderItem
@@ -18,21 +17,22 @@ const shortid = require('shortid');
  */
 
 /**
- * @param {boolean} [includeIdentifier]
+ * @param {string | null | undefined} [identifier]
  * @param {boolean} [allowEmptyPaymentObject]
  * @returns {Payment}
  */
-function createPaymentPart(includeIdentifier = true, allowEmptyPaymentObject = false) {
+function createPaymentPart(identifier, allowEmptyPaymentObject = false) {
   /** @type {Payment} */
   const payment = { '@type': 'Payment' };
-  if (includeIdentifier) {
-    payment.identifier = shortid.generate();
+  const hasIdentifier = !isNil(identifier);
+  if (hasIdentifier) {
+    payment.identifier = identifier;
   }
 
   const { paymentReconciliationDetails } = global.SELLER_CONFIG.primary;
 
   if (!paymentReconciliationDetails) {
-    if (!includeIdentifier) {
+    if (!hasIdentifier) {
       if (allowEmptyPaymentObject) {
         return payment;
       }