We deal with MCO's/insurance companies who send us remittance advice which can include multiple clients. We set up the MCO/Insurance as a client with multiple relationships, so we apply the payment to the correct client under the MCO/Insurance co. We are not able to apply an amount more than what is owed to the specific client. So for any "overpayments" I have to keep a separate spreadsheet to know who the overpayment pertains to.