Hello,
I checked the BAPI and sadly it has no documentation.If its the correct BAPI then check below things-
1. Are you passing 'X' in the corresponding update structure(PRHEADERX) fields and keeping test run flag as space TESTRUN.
2. Try calling 'BAPI_TRANSACTION_COMMIT' after the run of 'BAPI_PR_CREATE' BAPI.
3. Check the return table 'RETURN' and tell us the error captured in it.
Assumption: You are successfully able to maintain profitability segment via transaction code /online mode.
BR.