Hello, Faisal.
Please clarify my doubts.
Now you can find business partner number (from BUPA_GENERAL_CALLBACK). But from here you can not create activity because commit work doesn't happen, as a result the partner hasn't been created yet, and standard check in activity creation fails because of this? Am I right?
One approach I'd try is to start some z-function module in separate task in background and implement the logic of activity creation there. And I would wait for appearance of this BP in but000 in this module. Then would proceed with activity creation. Not the most beautiful approach. But sometimes there are no other ways.