You enter a two character key in the Posting key field in order to specify how a line item is posted. The following figure illustrates the posting key function:

The most important posting keys for vendor line items are:

• 31 Invoice
• 21 Credit memo
• 25 Outgoing payment

If you want to define other posting keys in your system, you can do so in Customizing.

The document type entered in the header and the posting key are related. The document type specifies which account types you can post to. The posting key specifies that you can post to a particular type of account. A posting key can only be entered for an account type which is permitted for that document type.