What happens when a customer pays more than the invoice?

The extra belongs to your customer, so DeskOps holds it as credit on their account and never sends it back on its own. The invoice shows how much was overpaid and what has happened to it since. Refund or keep it offers the way back that fits how they paid. A card or bank payment is refunded on that same payment. Cash or a check is something you hand back yourself; tell DeskOps how and it records it. Keeping it moves nothing at that moment; the credit remains available for a later invoice or refund. If the payment that caused the overpayment is undone, the unused credit is taken back and the invoice says so. The customer's receipt tells them the extra is held for them. The accountant package lists the credit you still hold at year end as money you owe.