A method for communicating financial transaction data between a plurality of computer devices using an interface module and an enhanced protocol is provided. The transaction is initiated by a cardholder at an input terminal using a transaction card for completing a purchase from a merchant. The method includes receiving at the interface module initial identification (ID) data from a merchant computer wherein the interface module is a computer module separate from the merchant computer, generating a first verification enrollment request (VEReq) message based on the initial ID data that includes at least one of a merchant identifier and an account number, transmitting the first VEReq message, receiving a verification enrollment response (VERes) message affirmatively verifying enrollment of the merchant in an express check out program, and generating at the interface module a payer authentication request (PAReq) message using the enhanced protocol that defines a first set of data field extensions.