Credit note rules require suppliers to issue and report credit notes in prescribed returns, limited if tax was passed on. Where a tax invoice overstates taxable value or tax, or goods are returned or deficient, the supplier may issue a credit note with prescribed particulars and must declare it in the return for the month of issue but not later than the September following the financial year or the relevant annual return, with tax liability adjusted as prescribed; no output tax reduction is allowed if tax incidence was passed to another person. If a tax invoice understates value or tax, the supplier must issue a debit note (including a supplementary invoice) and declare it in the return for the month of issue, with adjustment as prescribed.