Hello Guru 
I have a problem with substitution.
I wrote a substitution which should fill field BSEG-ABAPER (when user dont fill this field).
Unfortunately this field is obligatory.
When I am trying to post document and this field is empty system is giving error (Fill in all required entry fields).
Why system first check that I filled field (abaper) and then trying to use substitution?
I want first use substitution and then checks fields...
Thx in advance