How do I credit an invoice?

From the invoice itself. The amount defaults to what is left to credit and cannot go above it. You pick a reason from a fixed list: commercial correction, service not delivered, uncollectible, or contract rescinded. You can add one line of free text, which is printed on the PDF and cannot be changed afterwards. If nothing is owed, the credit sits on the client's account. Only the business owner can issue a credit note.