With synchronous processing, you should test register 15 after the request because the request may not have been accepted (register 15 contains 4) or because an error might have occurred (8 or 12):

         GET   RPL=REQPARMS
         LTR   15,15            Was request completed successfully?
         BNZ      REJFAIL       If branch is not taken, was request     x
                                accepted and completed successfully?
         ...
REJFAIL  ...