Substitution rule in OBBH for VF01/VF02 transaction

Hi,

I´ve created a substitution rule in OBBH ( Substitution in Accounting Focuments ) at callup point 0003 - document level - just to fill the BSEG-ZUONR field in FI billing doc using a user exit.

The problem is that when I create the billing document in VF01, the system create in memory the FI doc, pass through callup 0001 - header and 0002 - item, but skip the 0003 - document level.

Can anyone help me to understand what is happening? Is there another way to do this?

This is the prerequisite for my rule:

( SYST-TCODE = 'VF01' OR SYST-TCODE = 'VF02' ) AND

( BKPF-BLART = 'J1' OR BKPF-BLART = 'JI' )

In substitution I selected Only exit and filled with my user exit code.

tks.

Leo