# PayAI x402 Facilitator

> The production x402 payment facilitator operated by PayAI. It verifies and settles stablecoin micropayments over HTTP across Solana, Base, Polygon, Avalanche, Arbitrum, Sei, X Layer, and SKALE — so a service can charge per request and an agent can pay for one, without accounts or API keys.

## When to use the PayAI facilitator

This origin is an [x402](https://docs.payai.network//x402/introduction) payment facilitator. x402 revives the HTTP `402 Payment Required` status code: a server answers an unpaid request with `402` and machine-readable payment terms, the client signs a stablecoin payment, and the facilitator verifies and settles it on-chain. No accounts, no API keys, no card on file, no human in the loop.

Reach for it when you are doing any of these:

- **Charging for an API, MCP tool, or agent service per request.** Put x402 middleware in front of a route and point it at `https://facilitator.payai.network`. You get paid in USDC per call, with no signup flow for your buyers. Start at https://docs.payai.network//x402/servers/introduction.
- **Paying for a resource that returned HTTP 402.** Use an x402 client SDK; it reads the payment requirements, signs, and retries. Start at https://docs.payai.network//x402/clients/introduction.
- **Finding services an agent can buy right now.** Query `GET https://facilitator.payai.network/discovery/resources` for the live catalog of x402-payable HTTP endpoints and MCP tools, including their payment terms and, where published, their input and output schemas.
- **Settling agent payments on Solana.** PayAI is Solana-first and sponsors gas, so the payer needs only USDC — no SOL for fees. It also settles on Base, Polygon, Avalanche, Arbitrum, Sei, X Layer, and SKALE.
- **Checking which chains and schemes are live** before advertising payment terms: `GET https://facilitator.payai.network/supported`.
- **Testing an x402 integration end to end** against a real merchant that returns 402: https://x402.payai.network/.

Do not use it for: card payments, fiat payouts, bank transfers, custody of user funds, or subscription billing. It settles stablecoin micropayments over HTTP; it is not a payment processor for consumer checkout and it never holds merchant balances.

## How an agent should call this API

1. Read the [developer reference](https://facilitator.payai.network/developers), or the OpenAPI description at https://facilitator.payai.network/openapi.json — it documents every public operation with typed request and response schemas.
2. Call `GET https://facilitator.payai.network/supported` to pick a live network and scheme.
3. Call `POST https://facilitator.payai.network/verify` to check a signed payment, then `POST https://facilitator.payai.network/settle` to move funds.
4. Errors are always JSON, never HTML. `/verify` returns `{ isValid: false, invalidReason, invalidMessage }`; `/settle` returns `{ success: false, errorReason, errorMessage, transaction, network, payer }`. Every other endpoint and every unknown path returns RFC 9457 `application/problem+json`. Treat `errorReason: "settlement_pending"` as unresolved rather than failed, and re-submit the identical body to poll for the outcome.

`GET` endpoints need no authentication. `POST /verify` and `POST /settle` take an optional `Authorization: Bearer <api-key>` for credit accounting and dedicated settlement lanes; without one you are served on the free tier. Keys come from https://merchant.payai.network.

This API is versioned by the `x402Version` field in the request body, not by a URL path segment or a version header. There is no `/v1/` prefix.

## API surfaces on this origin

- [OpenAPI description](https://facilitator.payai.network/openapi.json): OpenAPI 3.1 spec for this API — verify, settle, supported networks, and Bazaar discovery. Canonical copy.
- [Developer reference](https://facilitator.payai.network/developers): endpoints, authentication, error model, versioning, and rate limits in one page. Also as [Markdown](https://facilitator.payai.network/developers.md).
- [About](https://facilitator.payai.network/about): who operates this service, what it does with funds, and how to reach a human. Also as [Markdown](https://facilitator.payai.network/about.md).
- [`GET /supported`](https://facilitator.payai.network/supported): live payment kinds, fee payers, and extensions.
- [`GET /discovery/resources`](https://facilitator.payai.network/discovery/resources): the PayAI Bazaar catalog of x402-payable resources.
- [`GET /discovery/stats`](https://facilitator.payai.network/discovery/stats): aggregate catalog and settlement statistics.
- [`GET /health`](https://facilitator.payai.network/health): liveness probe.

## Machine-readable surfaces

- [llms-full.txt](https://facilitator.payai.network/llms-full.txt): this guide plus the full developer reference inline.
- [ARD manifest](https://facilitator.payai.network/.well-known/ard.json): Agentic Resource Discovery entries for this API, the docs MCP server, and the Bazaar catalog. Also served at the predecessor path /.well-known/ai-catalog.json.
- [Pricing](https://facilitator.payai.network/pricing.md): what a settlement costs, in Markdown.
- [MCP manifest](https://facilitator.payai.network/.well-known/mcp.json)
- [AI catalog](https://facilitator.payai.network/.well-known/ai-catalog.json)
- [API catalog (RFC 9727)](https://facilitator.payai.network/.well-known/api-catalog)
- [security.txt (RFC 9116)](https://facilitator.payai.network/.well-known/security.txt)
- [Sitemap](https://facilitator.payai.network/sitemap.xml)

Every page on this origin also serves Markdown. Request it with `Accept: text/markdown`, or append `.md` to the path (for example https://facilitator.payai.network/developers.md).

## MCP

PayAI operates two MCP servers. The facilitator itself is available over Streamable HTTP at https://facilitator.payai.network/mcp with no authentication; its tools verify and settle payments, report supported payment kinds, and browse discovery data — `settle_payment` moves real funds. The documentation search server at https://docs.payai.network//mcp also uses Streamable HTTP with no authentication and answers questions from the PayAI documentation corpus.

## Elsewhere

- [PayAI](https://payai.network/): what PayAI is and who it is for.
- [Documentation](https://docs.payai.network/): quickstarts, protocol reference, and supported networks.
- [Supported networks](https://docs.payai.network//x402/supported-networks): every chain and asset this facilitator settles.
- [Pricing](https://docs.payai.network//x402/facilitators/pricing): free tier and per-settlement pricing.
- [Merchant portal](https://merchant.payai.network): API keys, credits, usage, and auto top-up.
- [x402 Echo Merchant](https://x402.payai.network/): live test merchant that returns HTTP 402.
- [GitHub](https://github.com/PayAINetwork): open-source SDKs, integrations, and examples.
- [Blog](https://blog.payai.network): product and ecosystem updates.

## Contact

- Email: info@payai.network
- Discord: https://discord.gg/eWJRwMpebQ
- X: https://x.com/PayAINetwork