Tag Card Architecture

A card payment looks simple from the outside. A customer taps a card. The terminal displays “Approved.” The merchant continues serving the next customer. But underneath that two-second interaction is a global messaging protocol that allows thousands of independent financial…

A coffee shop in Tokyo accepts a Visa card issued by a small credit union in Ohio. The barista has never heard of the credit union. The credit union has never heard of the coffee shop. There is no direct…