diff --git a/api.planx.uk/modules/file/service/uploadFile.ts b/api.planx.uk/modules/file/service/uploadFile.ts
index a6ee74227b..ead3cee9af 100644
--- a/api.planx.uk/modules/file/service/uploadFile.ts
+++ b/api.planx.uk/modules/file/service/uploadFile.ts
@@ -79,9 +79,9 @@ export function generateFileParams(
     ACL: "public-read",
     Bucket: process.env.AWS_S3_BUCKET,
     Key: key,
-    Body: file.buffer || JSON.stringify(file),
+    Body: file.buffer,
     ContentDisposition: `inline;filename="${filename}"`,
-    ContentType: file.mimetype || "application/json",
+    ContentType: file.mimetype,
   };
 
   return {
diff --git a/api.planx.uk/modules/file/service/utils.ts b/api.planx.uk/modules/file/service/utils.ts
index 0f95e170e5..85e58cd110 100644
--- a/api.planx.uk/modules/file/service/utils.ts
+++ b/api.planx.uk/modules/file/service/utils.ts
@@ -1,5 +1,6 @@
 import { S3 } from "@aws-sdk/client-s3";
 import { isLiveEnv } from "../../../helpers.js";
+import { Readable } from "stream";
 
 export function s3Factory() {
   return new S3({
@@ -40,3 +41,23 @@ export function getS3KeyFromURL(fileURL: string): string {
   const key = [folder, file].map(decodeURIComponent).join("/");
   return key;
 }
+
+export const convertObjectToMulterJSONFile = (
+  data: Record<string, unknown>,
+  fileName: string,
+): Express.Multer.File => {
+  const buffer = Buffer.from(JSON.stringify(data));
+
+  return {
+    buffer: buffer,
+    originalname: fileName,
+    mimetype: "application/json",
+    size: buffer.length,
+    fieldname: "file",
+    encoding: "7bit",
+    stream: Readable.from(buffer),
+    destination: "",
+    filename: "",
+    path: "",
+  };
+};
diff --git a/api.planx.uk/modules/send/s3/index.ts b/api.planx.uk/modules/send/s3/index.ts
index 6f7186ae8b..2a414d4e94 100644
--- a/api.planx.uk/modules/send/s3/index.ts
+++ b/api.planx.uk/modules/send/s3/index.ts
@@ -8,6 +8,7 @@ import { uploadPrivateFile } from "../../file/service/uploadFile.js";
 import { markSessionAsSubmitted } from "../../saveAndReturn/service/utils.js";
 import { isApplicationTypeSupported } from "../utils/helpers.js";
 import type { SendIntegrationController } from "../types.js";
+import { convertObjectToMulterJSONFile } from "../../file/service/utils.js";
 
 interface CreateS3Application {
   insertS3Application: {
@@ -44,16 +45,16 @@ const sendToS3: SendIntegrationController = async (_req, res, next) => {
     const flowName = session?.flow?.name;
 
     // Generate the ODP Schema JSON, skipping validation if not a supported application type
-    const doValidation = isApplicationTypeSupported(passport);
-    const exportData = doValidation
-      ? await $api.export.digitalPlanningDataPayload(sessionId)
-      : await $api.export.digitalPlanningDataPayload(sessionId, true);
+    const skipValidation = !isApplicationTypeSupported(passport);
+    const exportData = await $api.export.digitalPlanningDataPayload(
+      sessionId,
+      skipValidation,
+    );
 
     // Create and upload the data as an S3 file
-    const { fileUrl } = await uploadPrivateFile(
-      exportData,
-      `${sessionId}.json`,
-    );
+    const filename = `${sessionId}.json`;
+    const file = convertObjectToMulterJSONFile(exportData, filename);
+    const { fileUrl } = await uploadPrivateFile(file, filename);
 
     // Send a notification with the file URL to the Power Automate webhook
     const webhookRequest: AxiosRequestConfig = {
@@ -69,7 +70,7 @@ const sendToS3: SendIntegrationController = async (_req, res, next) => {
         service: flowName,
         environment: env,
         file: fileUrl,
-        payload: doValidation ? "Validated ODP Schema" : "Discretionary",
+        payload: skipValidation ? "Discretionary" : "Validated ODP Schema",
       },
     };
     const webhookResponse = await axios(webhookRequest)
@@ -125,7 +126,7 @@ const sendToS3: SendIntegrationController = async (_req, res, next) => {
 
     res.status(200).send({
       message: `Successfully uploaded submission to S3: ${fileUrl}`,
-      payload: doValidation ? "Validated ODP Schema" : "Discretionary",
+      payload: skipValidation ? "Discretionary" : "Validated ODP Schema",
       webhookResponse: webhookResponse.axiosResponse.status,
       auditEntryId: webhookResponse.id,
     });