Facilitator & networks
Protocol versions, headers, networks, assets, the facilitator Swop settles through, and limits.
At a glance
| Value | |
|---|---|
| Protocol | x402, version 2 offers; version 1 payments accepted |
| Scheme | exact (EIP-3009 transferWithAuthorization) |
| Network | Base mainnet, eip155:8453 |
| Asset | USDC, 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913, 6 decimals |
| Facilitator | Coinbase Developer Platform (CDP) x402 facilitator |
| Discovery | CDP x402 Bazaar, indexed after a first paid settlement |
| Payment window | maxTimeoutSeconds: 300 |
| Max total per purchase | Under $1,000,000,000 (a precision guard, not a business limit) |
| Platform fee on agent payments | None at launch |
Headers
| Direction | v2 name | v1 name | Content |
|---|---|---|---|
| Server → agent | PAYMENT-REQUIRED | (body only) | Base64 JSON of the 402 challenge. The JSON body carries the same object |
| Agent → server | PAYMENT-SIGNATURE | X-PAYMENT | Base64 JSON payment. Swop accepts either name |
| Agent → server | X-ORDER | X-ORDER | Base64 JSON of options and shipping details, when needed. ?shipping= works too |
| Server → agent | PAYMENT-RESPONSE | X-PAYMENT-RESPONSE | Base64 JSON of the facilitator's settlement result. Both are sent |
The buy endpoint's CORS policy allows GET from any origin with these headers, and exposes the response headers, so browser-based agents can read them.
What changed between v1 and v2
| v1 | v2 | |
|---|---|---|
| Payment header | X-PAYMENT | PAYMENT-SIGNATURE |
| Settlement header | X-PAYMENT-RESPONSE | PAYMENT-RESPONSE |
| Network id | "base" | "eip155:8453" (CAIP-2) |
| Amount field | maxAmountRequired | amount |
| Resource | String on the offer | Object { url, description, mimeType } at the top level |
Swop's offers include both amount and maxAmountRequired (always equal), so a client on either version reads the right number. When Swop forwards a payment to the facilitator it mirrors the version the buyer used.
The facilitator
A facilitator is the service that checks an x402 payment (verify) and submits it on-chain (settle), so neither the seller nor the buyer has to run blockchain infrastructure or pay gas. Swop calls Coinbase's CDP facilitator for every agent purchase. The CDP facilitator also builds the x402 Bazaar: endpoints that include Bazaar metadata in their 402 responses are catalogued automatically after a paid settlement, which is how autonomous buying agents discover Swop sellers.
Planned
Swop intends to run its own facilitator so settlement doesn't depend on a third party. Nothing about the buyer or seller flow changes when it does.
Limits and safety
- Rate limits. Store listings share the general API limit; buy requests have a stricter per-client order limit. A
429means back off. - Stock. Checked before payment: a sold-out product answers
409and no money moves. - Idempotency. A payment that already settled can't create a second order. Retrying returns the first order with
duplicate: true. - No KYC on this rail. Sellers are paid in USDC without identity verification. Card payments are a separate rail with its own requirements, covered in Payments.
- Escrow for physical goods. Payment for a physical product is held and released after delivery is confirmed.