Help needed Urgently- Rebate based on collected amount

Question

Dear all,
I come across scenario while discussiion with client that they require rebate with collection. Details of the requirement are given below:
1. SAP rebates run on billed values & set the accrual in rebate agreement on the rate what we have specified in the rebate agreement. Requirement is that, If i have billed on 1000$ & my accrual value is 100$ with the rate of 10%. If i collected 800$ instead of 1000$, then i need to pay the accrual on the basis of 800$ not on the basis of 1000$. It means i have to adjust accrual amount on the basis of 800$. Conclusion is that i have to pay not 100$ accrual instead less then 100$ on the basis of 800$ which i collected.
2. In month 1 have billed on 5000$, my accrual amount is 500$ with rate of 10%. In the 2nd month i have to bill 1000$ and i have given an discount of 500$, it means my billed value is 500$ and my accrual amount is 50$@10%. In month 3 again i billed 500$ and my accrual amount is 50$@10%.
Requirement is that, when i am going to pay the accrual to client, i should pay correct accrual for which he is entitled for. Means i should pay 100$ accrual not 600$ because i have already given an discount of 500$. Discount which i have given already of 500$ should need to be offest with the first month accrual of 500$. So remaning accrual is 100$.
Great if somebody can help me out for the solutioning of the above requirements.

Answer 1

Thanks Ivano,
Somebody has started the conversation.
Let me put my questions again.
This requirement is nothing to do with Payment procedure in the agreement type.
1. In any month if i billed 1000$, so my account receivable would be 1000$. My rebate for that month is 100$ at the rate of 10%. During customer receipt if i collected against my invoice 900$ instead of 1000$, my accrual needs to be corrected 90$ instead of 100$.
I know this can not be fullfilled by standard SAP, by any thoughts on this welcomed.
2. I know Rebate can be settled partially or full settlement by payment method( by cheque, bank transfer, or by credit memo) we have configure in rebate agreement type. But here requirement is totally different.
Here, i need to pay the Rebate as a Discount instead of by cheque or by credit memo. While doing the partial or full settlement system will take into account collected accrual up to that day & apply as a discount to the final bill.
Scenario is like that sometimes customer asked to give us the discount on bill for whatever they accrued so far.
This is again cannot solved by standard SAP, but any thought by any body welcome. We have already thought that we need to enhance the solution.
Solution needed urgently.