Hello,
during invoice creation the billing block is checked in customizing copy control routine set in transaction VTFA. Example in the header copy routine 001:
IF VBAK-FAKSK NE SPACE.
SELECT SINGLE * FROM TVFSP WHERE FAKSP = VBAK-FAKSK
AND FKART = TVFK-FKART.
IF SY-SUBRC = 0.
PERFORM VBFS_HINZUFUEGEN USING '000000' '014' SPACE SPACE SPACE.
SY-SUBRC = 4.
Are you using the correct copy routines checking VBAK-FAKSK at header level and VBAP-FAKSP at item level ?
Best regards,
Ivano.