Credit note issuance allows suppliers to reduce tax liability for overstated invoices, subject to declaration and prescribed limits. Section 34 permits suppliers to issue credit notes when invoices overstate taxable value or tax, goods are returned, or supplies are deficient, and requires declaration of such credit notes in the return for the month of issue but not later than the September following the end of the financial year or the relevant annual return, with tax adjusted as prescribed; reduction is barred if tax and interest have been passed on. It requires issuance of debit notes (including supplementary invoices) where invoices understate value or tax, with declaration in the return for the month of issue and prescribed tax adjustment.