Answer
The raw response body from an outbound HTTP-connector Application Message is stored as a BLOB in the MESSAGE_VALUE column of the FNDCN_MESSAGE_BODY_TAB table, filtered by the specific APPLICATION_MESSAGE_ID and a REPLY=1 flag distinguishing the reply body from the original outbound request body. To process that reply entirely through configuration, without any Developer Studio code modification: create a Custom Event on FNDCN_APPLICATION_MESSAGE_TAB triggered on its STATE field, with a condition scoping it to your specific integration and to STATE='Finished'; have that event's action call a second event ASYNCHRONOUSLY via a background-job Deferred_Call, rather than acting directly, since the reply data isn't actually committed yet at the exact moment the first event fires off the application-message table update. That second, deferred event's own Event Action is where you actually query FNDCN_MESSAGE_BODY_TAB for the reply BLOB and process its content, converting it to XML or JSON and handling it with standard PL/SQL from there.