Hi Leo,
in B1 object call atom, please switch parameter "Stop processing if fails" towards #false.
In final atom0 handle the error accordingly to report it back to the web service caller.
Best regards
Bastian
P.S.: If "Stop processing if fails" is set to #true, the integration framework immediately stops the processing in case of synchronous web service inbound calls and skips the final atom0: Therefor you don't get any result message.