Credit notes and debit notes

Sometimes an invoice needs adjusting after it is issued. That is what credit and debit notes are for.

Credit note

You issue it when the invoice value goes down: a return, a discount, or an overcharge. It reduces your tax liability.

Debit note

You issue it when the invoice value goes up: an undercharge or extra supply. It increases the tax. Both must reference the original invoice and be reported in your returns.