The Sales Invoice and Accounting document are linked through the Object Key from the Accounting Document Header table and the Billing Document number from the Billing Document Header Data table.

Table VBRK (Billing Document: Header Data) is linked to table BKPF (Accounting Document Header) through the fields BKPF-AWKEY (Object key) and BKPF-AWTYP (Ref. procedure).

The Reference procedure field BKPF-AWTYP must be set to 'VBRK'.