What Agentic Commerce Protocol (ACP) is
The Agentic Commerce Protocol (ACP) is the checkout specification a seller implements so a buying agent can buy on the buyer's behalf: checkout session endpoints (create, update, retrieve, complete, cancel) versioned by an API-Version header, payment handlers negotiated per session, and a product feed. This surface implements the checkout session endpoints at API-Version 2026-04-17 as the specification read on 2026-11-05.
Payment is one handler, ai.agent-acp.x402: x402 version 2 on Base mainnet, USD Coin or Open USD, verified and settled through the facilitator. No card handler and no Stripe handler is offered. An agent that declares only handlers this seller does not take is told so on the session, and a completion against a handler the session does not offer answers the specification's unsupported error, never a success.
What is sold here is GreenCore's own: one metered call on the cosmetics door, delivered in the order with a signed receipt. The product feed carries the A2A hubs' priced catalogue — rows whose maker has put a list price on the record, keyed by GTIN with their claim status; those goods are sold by their makers, not through this checkout.
How an agent pays here
- 1 — GET /.well-known/acp.json for the version and services; the handler spec is at /acp/handlers/x402.
- 2 — POST /checkout_sessions with API-Version 2026-04-17, an Idempotency-Key, capabilities and the line item cosmetics-door-call — 201 with the session and its x402 requirements for the total.
- 3 — Sign one entry of the session's x402 requirements with the buyer's wallet.
- 4 — POST /checkout_sessions/{id}/complete with payment_data under handler x402_base: settled → completed, with the order, the delivery and the receipt; not settled → payment_declined, nothing charged.
- 5 — POST /checkout_sessions/{id}/cancel closes an open session.
Two offers
- One metered call on the cosmetics door — sold here; paid by x402, delivered in the order with a signed receipt
- A block of 100 calls on the cosmetics door — not sold through this checkout: no delivery for a block exists on the x402 rail
- Product — the cosmetics door: its statement at mcp.a2a-cosmetics.ai/health.json, read at the call, never copied.
- Machine copy — /offers.json
The receipt contract
Every receipt carries the payer, the transaction, the amount and asset, the resource, the rail, the host that issued it and the notice; the jwt verifies against /x402/jwks.json (kid a2ac-x402-receipts-2026-09) and the receipt resolves forever at /x402/receipt/{nonce}. A card-rail receipt, when those rails settle, carries the test-mode charge reference in the same shape.
This surface implements the rail it is named after. Nothing here is endorsed by any protocol's owner. Artificial intelligence makes mistakes. A2A Cosmetics is an information source, not a recommendation.
- Key — /x402/jwks.json · kid a2ac-x402-receipts-2026-09 · private half held by GreenCore Solutions Corp.
- Register — /x402/settled.json (this host, with the four-host total beside it)
The other three
- agent-x402.ai — x402
- agent-mpp.ai — Machine Payments Protocol (MPP)
- agent-ucp.ai — Universal Commerce Protocol (UCP)
- Every .ai host answers all four rails; each site explains the rail it is named after.