When applying payments to invoices or charges, the invoices and charges should show up based on ownership settings on the client record. If an invoice or charge is showing up that should not be paid by the payer, this could be due to settings on the client record.

1. In Records > Clients > open the client whose invoice or charge should not be showing up for that payer
2. Select the Statements tab
3. Ensure there is only 1 instance of each payer and/or delete an extraneous rows
If there are no extra rows, ensure the "Activity to Show" is set correctly for each payer, with "Only charges assigned directly to [Client]"
4. Save and close the client
5. Confirm the invoice or charge for the client in question is no longer showing up to be paid by the other client.