Here's what to do in case you'd like to change an invoice that you already marked as paid but later found out that the customer's check bounced, for example.

Delete Payments For the Invoice

Before editing a paid invoice, you need to remove the payments from your invoice.

IMPORTANT: If you remove a payment that your customer paid, please make sure to add the removed payment amount as a credit to the customer's credit balance.

First, click 'Payments' on the invoice detail page to remove payments.

And then remove the payments belonging to the invoice.

Once you remove all payments from an invoice, you can edit it again and re-send it to your customer.