Invoices and payments

An invoice is a demand for money. It has a number, a client, lines, a due date, and however many payments have landed against it.

Overdue is not a status you set

An invoice that has been sent, is past its due date and still owes money is overdue, everywhere it is displayed. Nobody marks it. Nobody forgets to.

Part payments

Record as many payments as actually arrive. The balance is the total minus what has been paid, and the invoice settles itself the moment that reaches zero.