Suppose you have paid a vendor bill in full, invoiced its items to your client and the client has paid the invoice in full. After some time, the vendor refunds some of the amount (due to some reason) and you want to return it to your client as well. How to handle this in Core?
When your vendor returns the amount, you can enter it as 'vendor credits' against that vendor, which can be used for vendor bill payments in the future. Check the Core Help for details on that. On the accounts receivable side, there is no direct way of paying back the client and linking it to the invoice. You can use credit memos to refund the client, but that won't affect your A/R. So the best way to handle this is to edit the payment from the client and reduce the amount in the Payments screen by the same amount, effectively refunding the client. Check the Core Help for details on editing payments. After this, the amount will show up as a balance on the invoice, which you can pay off using a credit or write-off payment.