Incoming messages are being ignored when endpoint_id is missing from the payload.
For example, this message is being ignored:
{ "event_id":"some-id", "timestamp":1604997708865, "event_type":"QA", "application":"QEApp", "tags":[ ], "event":{ "account_id":"6089719", "message":{ } } }

But when sending endpoint_id = null, it's not being ignored, for example:
{ "event_id":"some-id", "timestamp":1604997708865, "event_type":"QA", "application":"QEApp", "endpoint_id":null, "tags":[ ], "event":{ "account_id":"6089719", "message":{ } } }

It seems that the schema needs to define the endpoint_id to default = null:
https://github.com/RedHatInsights/notifications-backend/blob/master/src/main/resources/avro/action.avsc