Credit and debit notes: suppliers must issue and report adjustments in returns, with limits where tax is passed on. If an invoice overstated tax or goods are returned or deficient, the supplier may issue a credit note and must declare it in the return for the month issued but not later than the September following the financial year or on furnishing the annual return, with prescribed adjustment of tax; reduction is barred where tax and interest have been passed to another. If an invoice understated tax, the supplier must issue a debit note (including a supplementary invoice), declare it in the return for the month of issuance, and adjust tax as prescribed.