Blocking issue: REST inbound message not processed, blocking issue to go live 12.2.10, 3 questions?

Upgrading EBS 12.1 up tot 12.2.10.

This stuff, at the end blocking, happens while trying to enable (working in 12.1) EBS XML Gateway for incomming XML messages:

1. Messages sent through Postman are received and approved by the Oracle. You will receive status 1000 -- OK and a return message id

2. This message can be found in ECX_OXTA_LOGMSG.

3. If you're quick, you'll find this message in APPLSYS.ECX_INQUEUE, where it will disappear a moment later.

4. If you look in ECX_INBOUND_LOGS, you will also find the message with a status 2 and an error_id. Status 2 gives the impression that it comes from a workflow or concurrent request. These have the default status "0", "1" and "2"

5. This error_id is associated with ECX_ERROR_MSGS. Here you will find the error