In t.code VTFL, go to Item level and add value G or B for the field Pricing type (depending on your business requirements) and keep value blank or E for the field Price Source. Then test by creating new documents.
Also with the help of ABAP'er check whether any user exit is added in program MV61AFZA to deactivate new pricing determination in billing document. If added, those coding can be deactivated and you can test.
Regards,