Billing Block will not worked if you did not assign it
Define the possible block indicators in SM30 - V_TVFS
and
allocate them to the billing types concerned in SM30 - V_TVFSP.
Your Billing Block will not worked if you did not assigned it to the desired billing types.
You can auto block by :-
1. sales document type in transaction VOV8, fields Billing Block,
or
2. item categories in SM30 - V_TVAP, by filling the fields Billing Block.
