Which of the following functions does the Address Verification Service NOT provide?

The Address Verification Service (AVS) is primarily designed to enhance the security of payment transactions by verifying the address information provided by the cardholder with the address on file at the card issuer. The functions it provides include verifying the legitimacy of the cardholder by checking their address, matching the provided address against the cardholder's billing address, and confirming the address prior to the completion of a transaction.

The reason that guaranteeing the validity of the transaction is not one of the functions provided by AVS lies in the nature of the service itself. AVS can help reduce fraud by providing a level of assurance regarding the address associated with a card, but it does not guarantee that a transaction is valid. Validity can encompass various factors, including available funds, account status, or legitimacy of the transaction beyond just the address. Therefore, while AVS enhances transaction security through address verification, it does not serve as a guarantee for the overall validity of any transaction.