Debit Note
A debit note is a document issued to increase the amount owed on a previously issued invoice — for example, when additional charges are added after the original invoice was sent.
A debit note is the mirror image of a credit note: instead of reducing what a client owes, it increases it — typically used when you under-billed for something, need to add a previously omitted charge, or a price revision applies retroactively.
Like credit notes, debit notes should reference the original invoice, follow proper numbering, and be reported in your GST returns since they affect your GST liability.
Both credit and debit notes are far cleaner, from an accounting and audit standpoint, than simply reissuing a corrected invoice with the same number — that practice can create confusion (or worse, GST mismatches) down the line.