I use GnuCash to manage the finances for my small business. I offer prepaid accounts to my customers who don't want to be bothered with invoices or have a fixed service budget.
I have set up the accounts as liabilities, and it seems obvious that after posting the invoice, I can enter a payment that goes into the liability account to reduce its balance. However, what happens when I have an invoice of, say, $100, and a prepaid balance of $25? I need to deduct the $25 from the prepaid balance and then issue a bill for the remaining $75. However, when I print an invoice (even if it has payments against it), it shows the total due as the full amount of the invoice.
How can I alter the total due so that it shows the true balance of the invoice (that is: total invoice amount less payments against it)?