Explainer · TIER_B
What is a machine-payment rail?
The rules, asset, network and verifier that let software settle without a checkout page.
zFinia published 7 September 2026
A machine-payment rail is the combination of asset, network, challenge format and verifier that lets software settle without a human checkout page. x402 on Base USDC is one rail. MPP is another family. Cards-as-tokens are a third wrapping.
Cover the rail that is live. Do not pretend every 402 is the same protocol.