The AS2 transfer was created with direction set as 'Receive'.
In Gateway error messages will be:
HTTP111E (...) ClientXferRequest: error Couldn't initiate request (UNSUPPORTED DIRECTION).
SUP011W  (...) connection abort indication: reason="18, Internal FT error : event incoherent with treatment in progress" /prot.diag="0, No HTTP error" / error=12.

As protocol AS2 is using POST method, direction in AS2 transfers has to be 'Send' and mode 'Initiator'.