In the API docs for the Conversions API for Business Messaging, the user is instructed to include the whatsapp_business_account_id parameter alongside the ctwa_clid parameter, in order to attribute a Business Messaging conversion event correctly. To quote:

{
  "data": [
    {
      "event_name": "Purchase",
      "event_time": 1675999999,
      "action_source": "business_messaging",
      "messaging_channel": "whatsapp",
      "user_data": {
        "whatsapp_business_account_id": "<WHATSAPP_BUSINESS_ACCOUNT_ID>",
        "ctwa_clid": "ARAkLkA8rmlFeiCktEJQ-QTwRiyYHAFDLMNDBH0CD3qpjd0HR4irJ6LEkR7JwFF4XvnO2E4Nx0-eM-GABDLOPaOdRMv-_zfUQ2a", // <CLICK_TO_WHATSAPP_CLICK_ID>
      },
      "custom_data": {
        "currency": "USD",
        "value": 123
      }
    }
  ],
  "partner_agent": "<PARTNER_NAME>"
}

This field is required for sending events to the Conversions API, which will error if it’s not included. However, the JavaScript SDK doesn’t allow the user to include it, which makes it unusable for sending these kinds of events.

FWIW, this is the only place the field is documented. It should also be included in the Customer Information Parameters doc, and linked to from the Parameters doc. It should probably also be documented as required.

(PR to follow)