FB60 USER EXIT PROB

I am trying to use a user exit in FB60, The exit is F050S001 - EXIT_SAPLF050_002. I have created the include ZX050U01. I have entered my code. I created a project

in CMOD. When I run the trans FB6O and go to post the document my breakpoint is never hit, Is there something I am missing? Any suggestions? I am trying to give a warning message when there is a duplicate invoice enterd but only for trans FB60, FB65 and MIRO