Card Payment Rails: What Happens When You Tap

The tap is instant. The money is not. Card payments run on a machine most engineers never see: four parties exchanging promises in a second and settling cash days later in netted batches. This path maps who touches every transaction, the three clocks a payment runs on, the fee structure that quietly shapes entire business models, and the failure paths, declines, 3-D Secure and chargebacks, where payments work actually lives.