adding notification for migration to use new cloud events extension for event consumers

Author: abhupadh

src/pages/support/faq.md

@@ -74,6 +74,14 @@ If you are sure that the event provider can be deleted, then follow the steps do
 5. Delete the provider via the [provider API](/events/docs/api/#tag/Providers/operation/deleteProvider), using the ids noted in above steps.
 6. Repeat the above steps for all conflicting event providers and try deleting the project again. Your project deletion should now go through successfully.
 
+### Why do I see duplicate fields in the delivered payload for attributes recipient client id and event id?
+I/O Events sends cloud event payloads with some internal custom attributes like `event_id` (used for event tracking and debugging) and `recipient_client_id` (used by consumers for payload verification. see https://developer.adobe.com/events/docs/guides/#improved-and-resilient-security-verification-for-webhook-events). 
+Recently Adobe I/O Events has upgrade its tech stack with `Java 17` which includes using the latest version of cloud events sdk. Due to stricter validation for custom attributes of cloud events in the latest sdk (see [spec](https://github.com/cloudevents/spec/blob/v1.0/spec.md#attribute-naming-convention)), the above custom attributes naming is not valid and it fails during serialization. So, to release our java17 change with backward compatibility we are now delivering cloud events payload to consumers with two extra fields namely `eventid` and `recipientclientid` conforming to the cloud events spec. Don't be surprised if you see four such fields (existing  format - `event_id` , `recipient_client_id` and new compliant format `eventid`, `recipientclientid`) in the delivered event payload to your webhook and journaling.
+
+**Action for consumers** -
+If consumers are using any of the fields present in the delivered payload in this format `event_id` and `recipient_client_id`, they must change to use new format `eventid` , `recipientclientid`. We will ultimately get rid of those two fields in old format by **end of 2025** and only have the cloud events spec compliant attributes in the delivered payload going forward.
+
+
 ## Webhook FAQ
 
 ### What happens if my webhook is down? Why is my event registration marked as `Unstable`?