Hi
If you have Invoiced $100 of 10 pc to XYZ Company in which he wants to Return 1 pc of $10
but he hasn't done payment for 10 pc yet.
Solution - In standard business process you should create Return Sales Order- Inbound delivery- Credit Memo , here remember one thing while creating SR Order you should mention (Invoice No in field - Name is so) through which it could be easy to Accounts department at the time of issuing Credit Note or Reconciliation) of 1 pc once Credit memo is created then provide the documents to Concerned person (Accounts deptt) then inform Customer to pay Only $90 for 9 pc although you have created Invoice $100 & can provide Credit Note of $10 hence matter could be solved .
Thanks
Kamlesh