Credit and debit notes: adjust taxable liability when invoices are corrected, with specified return declaration and adjustment rules. Credit notes correct overstated taxable value or tax, or address returned or deficient supplies; they must contain prescribed particulars and be declared in the return for the month issued, but not later than the September after the financial year or upon furnishing the annual return, with tax liability adjusted as prescribed; reduction is prohibited if tax incidence was passed to another. Debit notes (including supplementary invoices) must be issued for understated taxable value or tax, declared in the return for the month of issue, and the tax liability adjusted as prescribed.