Frequently Asked Questions
Everything you need to know about PayAPI Market, the x402 marketplace for AI agents.
Last updated: 2026-10-24
General
What is an x402 marketplace?
An x402 marketplace is a catalogue of APIs that accept x402 payments, so an AI agent can find a service and pay for each call in USDC without an account or API key. PayAPI Market is one. Discovery is free, and the agent pays the provider directly on the listing's own HTTP 402.
What is PayAPI Market?
PayAPI Market is a pay-per-call API marketplace for AI agents, built on x402. Providers list an API for free and keep 100% of what each call earns. Agents search the catalogue for free, then pay each provider per request in USDC on Base, Solana or Algorand, where a listing offers it, with no API key, account or subscription.
What is the x402 protocol?
x402 is an open payment protocol built on HTTP 402 Payment Required. When an agent calls a paid endpoint without paying, the server replies 402 with the price, token, network and wallet. The agent signs a USDC payment, retries the request and gets the response. No account, API key or OAuth flow is needed.
How much does PayAPI Market cost?
Listing is free and there is no per-request fee, so providers keep 100% of what each call earns. Searching the catalogue is free for agents too. Buyers pay only the provider's own per-call price in USDC, shown on the listing and in the 402 challenge before any money moves. There are no subscriptions.
How do AI agents discover APIs on PayAPI Market?
Agents connect to one MCP server at https://payapi.market/mcp, which has three free tools: search_apis, list_apis and get_api. Plain HTTP works too, at /agent/search, /agent/list and /agent/get. Discovery never charges and never returns a 402. The agent then calls the provider's own endpoint and pays its HTTP 402 directly.
What does settlement-verified mean?
It means PayAPI Market paid a real call on one specific route from its own wallet, got real product back, and there is an on-chain USDC receipt that anyone can check. It is not a health ping. Verification covers the route we paid, not the whole listing: a listing with 10 routes and one paid route reads 1 of 10 routes settlement-verified. Listed APIs answer a valid 402 but have not been paid for yet.
How is PayAPI Market different from RapidAPI?
RapidAPI is built for human developers: you sign up, get an API key and buy plans, and RapidAPI's own docs state a 25% marketplace fee on payments through its hub. PayAPI Market is built for AI agents. There is no key or account, agents pay per call in USDC on Base, Solana or Algorand, and providers keep 100%.
How is PayAPI Market different from Coinbase Bazaar or x402scan?
Coinbase's x402 Bazaar is a catalogue of x402 services discovered through the CDP Facilitator, and x402scan is an independent explorer that indexes x402 endpoints and payments. PayAPI Market is a curated marketplace where a verified badge means we paid for a real call and got real product back, with an on-chain receipt.
What APIs are available on PayAPI Market?
PayAPI Market lists APIs across property, weather, companies, vehicles, finance, HMO licensing, waste collection, air quality, text analytics and more. Every listing is billed per request in USDC, and settlement-verified listings carry an on-chain receipt. Browse the full catalogue at payapi.market/marketplace, or search it free over MCP.
For AI Agents
Do I really not need an API key?
Correct. With x402 the payment is the authentication. The provider's endpoint replies HTTP 402 with the price and wallet, your agent signs a USDC payment authorisation, and the request is retried with it attached. The provider's facilitator settles it on-chain, so your agent needs no API key and no account. On Base it needs no ETH for gas either.
What does a call cost?
Each provider sets its own price per call, and the listing shows it. Prices start at fractions of a cent, and some specialist routes cost more. The exact USDC amount also arrives in the 402 challenge before any money moves, so your agent can check the price and refuse anything above its cap.
Which wallet should my agent use?
Any EVM wallet that holds USDC on Base, such as Coinbase Wallet, MetaMask or your agent's own key. Use a dedicated wallet with a small balance, for example $5. An x402 client library such as @x402/fetch for JavaScript or the x402 package for Python signs each payment for you. Base works on every listing. For a listing that also accepts Algorand, an Algorand account holding Circle USDC (ASA 31566704) works too.
How do I use PayAPI Market from Claude or Cursor?
Add one entry to your MCP config, "mcpServers": { "payapi": { "url": "https://payapi.market/mcp" } }, then restart the client. Your agent gets three free tools: search_apis, list_apis and get_api. To pay for a call, it also needs an x402-capable client and a wallet holding USDC on Base.
Can I cap what my agent spends?
Yes. Every 402 states the exact USDC amount before any money moves, so your agent or x402 client can refuse any call above a per-call limit you set. Fund a dedicated wallet with a small balance, so total spend can never exceed what you put in. There are no subscriptions or recurring charges.
What happens if a call fails after I pay?
PayAPI Market is not in the payment path, so it cannot refund or reverse a payment, and an x402 payment is final once it settles on-chain. Many providers settle only after a successful response, but that is each provider's choice. Start with settlement-verified listings and check the reliability score before you call.
Which networks can agents pay on?
Every listing accepts USDC on Base, so an agent with Base USDC can pay any listing. Some listings also accept Circle-native USDC on Algorand (ASA 31566704) or USDC on Solana on the same route, and their 402 challenge shows it. Solana and Algorand are extra options on a Base listing, not a replacement. We count a network as verified for a listing only after we have paid a route on it, and the listing shows which networks are verified.
Is it safe to let an agent pay for APIs?
x402 has no chargebacks, so safety comes from limits you control. Use a dedicated wallet with a small balance, set a per-call price cap, and prefer settlement-verified listings, where PayAPI Market paid a real call and got real product back. Your agent signs each payment itself, and PayAPI Market never holds your funds.
For API Providers
How do I list my API on PayAPI Market?
Go to https://payapi.market/list and give a durable URL, the paid route, a Base USDC wallet you control and the price your live 402 returns. Automated checks run first, then a person reviews it, and you get one email with the result. Listing is free. Tunnels and sandbox hosts are not accepted.
Does PayAPI Market take a cut?
No. Listing is free and there is no per-request fee. Each call is paid by the agent straight to the wallet in your 402 challenge, settled in USDC on Base, Solana or Algorand if your route accepts them, so you keep 100% of what the call earns. PayAPI Market is not in the payment path and never holds your funds.
What does settlement-verified mean for my listing?
After review, PayAPI Market pays one cheap call on one route, up to $0.10, from its own wallet. If real product comes back and the money lands in your listed wallet, the listing goes live with a settlement-verified badge. The badge is that on-chain receipt on Base, not a health ping. It covers the route we paid. Other routes on your listing stay unverified until paid.
Do I need to write Solidity or any blockchain code?
No. You need a route that answers unpaid requests with a valid x402 HTTP 402 challenge that pays your Base USDC wallet. Standard x402 middleware for TypeScript, Python or Go handles the challenge, payment check and settlement, so you set a price per route and keep your existing API code.
Can I keep my existing API and just add x402 in front of it?
Yes. You can add x402 middleware to your current server, or run a thin gateway in front of it that returns the 402 and forwards paid requests. Your application code can stay as it is. What matters for listing is a durable URL whose paid route returns a valid 402 to your wallet.
How do I get paid out from USDC to my bank?
Payments arrive as USDC in the wallet you listed for that network, call by call, with no monthly batching. To turn USDC into pounds or dollars, send it to an exchange that supports USDC on Base, such as Coinbase, and withdraw to your bank. PayAPI Market never holds your funds at any point.
What happens if my API goes down?
You stop earning while it is down, and PayAPI Market never charges you for downtime. Every search and listing result carries a reliability score built from paid verifications, health history and payment-address integrity, so sustained failures lower how agents see your listing. Fix the route and the score can recover.
For Enterprises
Are payments custodial?
No. Each call is paid in USDC from your agent's own wallet straight to the provider's wallet, on Base or on another network the listing offers. PayAPI Market is not in the payment path and never holds or routes your funds. Every settled call leaves an on-chain receipt that your finance team can check on a block explorer.
Do we need a contract or a procurement process?
No contract is needed to use the marketplace. Discovery is free, and your agents pay providers per call in USDC with no subscription, minimum spend or invoice. If your organisation has specific legal, finance or procurement requirements, email hello@payapi.market and describe what you need.
How do we control what our agents spend?
Give each agent a dedicated wallet with a bounded USDC balance on Base, so spend can never exceed what you fund. Every 402 states the exact price before any money moves, so your agent or x402 client can enforce a per-call cap. There are no recurring charges to cancel and no seats to manage.
Is there a per-request fee at high volume?
No. PayAPI Market charges no per-request fee at any volume, and providers keep 100% of every settled call. Your agents pay only each provider's listed per-call price in USDC on Base. If you have specific requirements at scale, email hello@payapi.market and describe your use case.
Who is responsible for an API's uptime?
Each provider runs its own API and is responsible for its uptime. PayAPI Market runs the free discovery layer and shows a reliability score on every search and listing result, built from paid verifications, health history and payment-address integrity, so your agents can avoid weak listings before they spend anything.
For Developers
Where are the official x402 SDKs?
The x402 reference SDKs cover TypeScript, Python and Go. For buyers, @x402/fetch with @x402/evm on npm and the x402 package on PyPI are common starting points. The spec and SDK source live at github.com/x402-foundation/x402, and community libraries cover other languages such as Rust.
Is there an open spec?
Yes. The x402 specification is open and lives at github.com/x402-foundation/x402, with documentation at docs.x402.org. The MCP specification is at modelcontextprotocol.io. Both are versioned. PayAPI Market uses MCP for free discovery and leaves payment to each provider's own x402 HTTP 402 challenge.
Can I run my own facilitator?
Yes. x402 is permissionless, so anyone can run a facilitator, and the docs at docs.x402.org list options. For PayAPI Market, what matters is that your paid route returns a valid 402 for USDC on Base to your listed wallet, and delivers real product once the call is paid.
Are there example agents I can fork?
Yes. A worked example of the whole loop, from connecting to https://payapi.market/mcp through to an on-chain receipt on Base, is at https://payapi.market/how-an-agent-finds-payapi. Each listing page also shows ready-to-run JavaScript and Python snippets for calling and paying that API with x402.
Pricing
Is listing really free?
Yes. Listing is free with no per-request fee. Providers keep 100% of what the call earns.
What does PayAPI Market charge providers?
Nothing per request. 100% of every x402 settlement goes directly to your wallet. USDC routes from the paying agent to your own wallet via the CDP Facilitator, and PayAPI Market never takes a cut on-chain. No invoicing, no monthly bill, no surprise fees.
Do I need a crypto wallet to get paid?
Yes. Payments settle as USDC on Base. You provide a Base wallet address at listing time, plus an optional Algorand address if your route also accepts Circle USDC on Algorand. Off-ramp to USD is available through any USDC-supported exchange or bank on-ramp like Coinbase.
Can I change pricing per endpoint?
Yes. Each route can have its own x402 price, set in your own server's x402 configuration. Your live 402 challenge is the source of truth, so the price on your PayAPI Market listing must match what the 402 returns. If you change the price, update your listing to match.
Do buyers pay monthly subscriptions?
No. The whole point of x402 is pay-per-request. AI agents pay only for the calls they make, in USDC, with no minimum spend and no accounts. This makes your API instantly usable by any agent on the network.
Listing Your API
What happens after I submit?
Automated checks run first (host durability, a real 402, payTo matches the wallet you entered). Then a human reviews. You get one email with the result. Live, needs a fix, or cannot test. There is no separate "we got it" mail.
Do I pay to list?
No. Listing is free. Providers keep 100% of each settled call.
What will you pay on my API?
One cheap canary on one route, up to $0.10, from our wallet. If that call returns real product and the money landed on your listed wallet, the listing can go live with a settlement-verified badge. The badge is that receipt, not a health ping.
My URL passed the check. Is it verified?
We will pay this exact URL once, up to $0.10. The badge is for the JSON that comes back after pay, not for the 402.
Do I need a transaction hash?
Optional. If you already settled a payment on this route, paste the Base tx hash and we check it first. Without one, we still create the listing as pending and verify it ourselves with one paid call (cap $0.10).
What gets bounced?
Ephemeral hosts (trycloudflare, ngrok, sslip, random zrok shares). Prepaid credits instead of per-call x402. A challenge payTo that is not the wallet on the form. A second listing that is the same product or a sub-path of one already live. extra.name must be "USD Coin" on Base USDC or settlement fails.
What do I need on the form?
A durable URL, the paid route, a Base USDC wallet you control, and a price that matches the live 402. Wallet is required. Sandbox and tunnel hosts are blocked.
My route also takes Solana USDC. Where does that go?
In the optional Solana payTo box under the Base wallet, only if this same paid route already accepts Solana USDC. Your Base 402 still decides the submit. We verify Solana only after a paid canary, so this box does not badge the card.
Why was my URL rejected?
We call it unpaid before a row is created. Homepage, AppDeploy/Floot/Bonto shells, and a 402 with no Base USD Coin challenge all fail here. The paid route has to 402 to your wallet. Any funded Base wallet that signs the 402 must receive the product. No allowlist, no API key, no signup.
How do agents find it once it is live?
Search is free at https://payapi.market/mcp. Put this in a README: url https://payapi.market/mcp
Verification
What does settlement-verified mean on PayAPI Market?
We paid a real call on one route of the listing from our own wallet, with a signed x402 payment in USDC on Base, Solana or Algorand. The payment settled on-chain, the USDC reached the provider wallet on the listing, and the route returned real product. The listing links the transaction so anyone can check it. It is not a health ping.
How is that different from a health check?
A health check or a 402 check shows that an endpoint is up and asks for payment correctly. Nothing is paid. Settlement-verified means a payment actually settled and the product came back, with the receipt published.
Where can I see the receipts?
Every verified listing shows its paid route and transaction hash. Exports of the paid routes are at payapi.market/verified-routes.csv and payapi.market/verified-routes.json, and /agent/get returns verified_routes with a receipt link for each paid route.
Does the badge cover every route on a listing?
No. It covers the route we paid. A listing with 10 routes and one paid route reads 1 of 10 routes settlement-verified, and the listing page shows which route and its receipt.
Does verification cost the provider anything?
No. Listing is free, we pay for the verification call from our own wallet, and providers keep 100% of what each call earns.
Does a badge mean every future call will work?
It shows that a paid call settled and returned real product at the time on the receipt. A service can change after that, so the receipt date is published and agents should still set a spending cap.