A2A Pay

The five rails in plain words

• x402 — Live. A resource that costs money answers 402 with an offer; the agent signs the payment and repeats the call; a facilitator verifies and settles USDC on Base; the receipt resolves forever. agent-x402.ai
• Machine Payments Protocol (MPP) — Built, dark. A 402 challenge in a WWW-Authenticate: Payment header, a credential in Authorization: Payment, a Payment-Receipt on success. Dark until a card method can settle. agent-mpp.ai
• Universal Commerce Protocol (UCP) — Built, dark. A business profile at /.well-known/ucp and a checkout session over REST: create, update, complete, cancel. Dark until a payment handler can settle; no profile is published before. agent-ucp.ai
• Agentic Commerce Protocol (ACP) — Built, dark. A product feed and checkout sessions versioned by an API-Version header; a delegated payment token from the platform. Dark until it can settle; no feed is served before. agent-acp.ai
• Agent Payments Protocol (AP2) — Declared on the card. AP2 has no zone: it sits on the hub's Agent Card as a declared payment method; joining is the CEO's ruling. a2a-cosmetics.ai/.well-known/agent-card.json

One line on all five

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