How to activate Substitutions?

Hi Friends,

I have created a substitution in the WBS Element level of Project Systems in GGB1 transaction. And i have substituted a custom field by Exit. I have created my own subroutine U902 in ZSXE_SUBSTITUTIONS. But this subroutine is not getting called. There is this include program GBTALFIB where the perform statements for these subroutines are generated. This happens when we run the RGUGBR00 program i guess. But my exit is not getting a perform statement here in this program.

Any input on this would be of great help.

Thanks and Regards,

Tamilarasan.