SAP Message RP651 - Debit memo procedure is not permitted for payment method &1, country &2

Diagnosis
You have set the 'Automatic Debit Authorization' indicator for a bankdetails type that is not the main bank details. The debit memoprocedure can only be used for the main bank details.

Procedure
Delete the entry in the 'Automatic Debit Authorization' field or changethe bank details type.