Failing Idoc Based on Posts Goods Issue

Hi experts,

I have a requirement where I need to check whether a STO exists for the idoc PORDCR102. Another requirement is to check Post Goods Issue is present. If STO exists and PGI exists, I need to fail the idoc. How to do this(both failing idoc and checking how PGI exists). I am using the user exit EXIT_SAPL2012_001 for this purpose.

Regards,

Sajith