Solution : https://service.sap.com/sap/support/notes/360478 (SAP Service marketplace login required)
Key words :
additional key words, billing plan, payment requests, sales order, system calculates, credit block, credit blocked, payment request, vbak-amtbl, real settlement
Related Notes :
399574 | Incorrect credit value in VKM1-4 with billing plan |
378398 | Credit update for down payment requests |