Solution : https://service.sap.com/sap/support/notes/74020 (SAP Service marketplace login required)
Key words : 
additional key words volume-based rebate purchasing, updating vendor business volume, accrued income remain visible, customizing condition type, accrued income mechanism, subsequent settlement statistics, condition type, accrued income, subsequent settlement, accured income
Related Notes : 
       
| 40147 | Collective note: Subsequent settlement (Purch.) Release 3.0 |