Hi Ruud,
In standard it uses in the copy control the requirement 003 on header for delivery-related billing.
Among other things this contains:
IF VBUK-WBSTK NA ' C'.
PERFORM VBFS_HINZUFUEGEN USING '000000' '066' SPACE SPACE SPACE.
SY-SUBRC = 4.
Which means, only if the goods movement status of the delivery is C (completed) or
blank (nor relevant for goods movement) is it possible to create the invoice.
So if you are using a material not relevant for goods movement, the billing is
allowed. This is the standard system behaviour. If you would like to
change this, either set the material relevant for goods movement or create your
own copy requirement.
Regards,
Alex