Payment document ZP is clearing customer credit memo DG and customer invoice RV separately with out posting the net amount of both the documents in F110 run

Hello All,

The customer has been posted with a invoice and credit memo and when the APP runs the customer have been cleared separately with 2 same payment document ZP?

Example:

Customer :                                XXXXX

Invoice :                                    100$

Customer credit memo:               -10$.

Total to be received from customer 90$.

When APP is run  2 payment document (ZP) is created for both the above documents and cleared.i,e

ZP 0000000001  posted with 100$ clearing the invoice. and

ZP 0000000001 posted with 10$   clearing the Customer credit memo.

However the requirement is to have one ZP document of 90$ clearing both the invoice and customer credit memo. Can anyone please let me know on what scenario does this happen?