51. Credit and debit notes.- Where a tax invoice has been issued in respect of a sale and (a) the amount shown as tax in that tax invoice exceeds the tax payable in respect of the sale, the dealer shall provide the purchaser with a credit note, containing such particulars as may be prescribed; or (b) the tax payable in respect of the sale exceeds the amount shown as tax on the tax invoice, the dealer shall provide the purchaser with a debit note, containing such particulars as may be prescribed. | 
