A ‘Posting Key’ (Transaction Code is OB41) in SAP is a 2-digit alphanumeric key that controls the entry of line items. SAP comes with many posting keys for meeting the different business transaction requirements: 40 (GL debit), 50 (GL credit), 01 (customer invoice), 11 (customer credit memo), 21 (vendor credit memo), 31 (vendor payment), etc.
The posting key determines:
- What account can be posted to
- Which side of the account (debit or credit) to be posted to, and
- What ‘layout’ screen needs to be used for that particular transaction.
It is a normal practice not to change any of the default posting keys in the system, as
you would very rarely require additional posting keys.