SAP Note 12999 - Posting period in SD billing header not filled

Symptom:

Field posting period in the SD billing document (VF01/VF02/VF03) after
selecting Header -> Detail is always 0, even when the document has
already been forwarded to accounting.

Cause and prerequisites

The field is not used yet.

Solution
Look at the posting period by selecting the view Accounting, Document
header.

Key word: Posting period