Hi @bonsai 

Check Outbound HTTP Requests.

To check the Outbound HTTP logs.

 Filter Navigator -> Outbound HTTP Requests.

Locate the outbound call that was made. (search by URL , by hostname if possible and probable time)

Open the log record

Check two tab is there  Request and response. You will able to see payload there.

If full payload you are not able to see, there is some properties needs to update (which you can do in sub-prod) temporarily and debug the issue.