Matching of credit notes governs supplier output tax liability; unresolved mismatches trigger additions and interest obligations. Credit notes issued by a supplier must be matched with corresponding reductions claimed by recipients; matched reductions are accepted and communicated. Discrepancies where supplier reductions exceed recipient declarations, or where recipients fail to declare credit notes, are communicated to both parties and unrectified amounts are added to the supplier's output tax liability in the succeeding return. Duplication of reduction claims is communicated and added to the supplier's liability for the month of communication. Added amounts attract interest from the date of the original claim until addition; accepted subsequent declarations permit recovery of the added amount and refund of interest to the supplier, limited to interest paid by the recipient.