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You can pay an AI agent or paid API in USDC through x402 without creating an account, API key, subscription, or checkout session. The service sends a payment challenge in an HTTP 402 Payment Required response; a funded wallet signs the requested payment, and the client retries the request with proof of payment. You still need a wallet that can sign transactions, and you should inspect the live payment terms before approving anything.
This model is useful for one-off calls, automated agent workflows, and services that do not want to maintain customer accounts. It is not a promise that every HTTP 402 endpoint is compatible, that every answer is accurate, or that a completed payment can be reversed. The practical discipline is simple: discover a service, read its challenge, cap the amount, sign locally, retain the receipt, and evaluate the returned result.
What does x402 do when you pay an AI agent?
x402 is an open payment protocol that uses the HTTP status code 402 Payment Required to tell a client how to pay for a request. Instead of signing up for a service first, the client receives machine-readable payment requirements, authorizes the payment through a wallet, and retries the request with payment proof. The service returns the requested data after the payment is verified and settled.
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That makes payment function as the credential for an individual request. It removes account setup from the payment flow, but it does not remove the need to decide whether a service is trustworthy, whether its response is useful, or whether the requested price is acceptable. An agent can therefore call a paid model, data API, or digital service on demand, paying only for the invocation rather than opening a recurring subscription.
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What “no accounts” actually means
The buyer does not need a merchant login, API key, subscription record, or browser session for the x402 exchange. The payment authorization is attached to the request instead. “No accounts” does not mean “no identity or state anywhere”: your wallet still controls funds and a provider may keep transaction, purchase, or service records. It also does not mean a provider has no policies. The endpoint can still impose request, content, rate, or purchasing rules.
What you need before making a payment
- A URL for an x402-enabled endpoint, or a service listing that points you to one.
- A wallet that holds USDC and can sign the payment authorization. The recommended pattern is local signing: your runtime holds the wallet key, and the seller verifies the signature rather than receiving your private key.
- A client capable of making the request and retrying after a payment challenge. The documented Coinbase agentic-wallet CLI provides one command-line route.
- A spending limit you are willing to authorize, plus a way to retain the payment response or transaction hash for reconciliation.
- A process for judging whether the result is worth the quoted amount. Payment proves authorization and settlement; it does not prove that an AI answer is true or that a data feed is complete.
How do the five x402 commands work?
The documented CLI has one command with options, not five separate payment programs. These five invocations cover a basic request, a spending cap, a POST body, query and header values, and JSON output. They use the documented entry point npx awal@2.12.1 x402 pay <url>. Pinning the version shown in the reference makes the syntax explicit; command versions and supported networks can change, so check the current command reference when you deploy.
1. Pay for a URL using its payment challenge
npx awal@2.12.1 x402 pay <url>Replace <url> with the paid endpoint. The client requests it and, if the endpoint responds with an x402 payment challenge, uses the challenge to determine what is being requested. Read the amount, asset, network, recipient, and facilitator details before proceeding. Do not assume every endpoint uses the same chain or payment terms.
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2. Set a maximum payment amount
npx awal@2.12.1 x402 pay <url> --max-amount 10000--max-amount sets a ceiling in USDC atomic units. The CLI reference gives these conversions: 1,000,000 units = $1.00; 100,000 = $0.10; 50,000 = $0.05; and 10,000 = $0.01. The example above therefore caps the payment at $0.01. Choose the cap before signing; if the service requests more, the cap helps prevent approving a payment above your limit.
Quote and inspect the actual requirement before signing. Amounts expressed in atomic units are easy to misread, and the cap should match the asset and payment requirement the endpoint presents. A cap is not a guarantee that the call will cost that amount: it is the most you allow the command to authorize. If the challenge is above the cap, investigate the price or deliberately choose a new limit; do not increase it automatically.
3. Send a POST request with a JSON body
npx awal@2.12.1 x402 pay <url> -X POST -d '{"prompt":"hello"}'Use this form when the endpoint expects a POST and a request body, such as a prompt. The method and payload are part of the service request; a payment challenge does not guarantee that an endpoint supports a particular method or body format. Check the service’s interface and use the expected payload.
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4. Add query parameters and an HTTP header
npx awal@2.12.1 x402 pay <url> -q '{"id":"42"}' -h '{"Accept":"application/json"}'This invocation supplies query data and an Accept header. Use the documented argument formats and ensure the endpoint accepts those values. Shell quoting matters: the CLI examples use single quotes around JSON strings, which also helps prevent shell expansion when values contain a dollar sign.
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Query values can select a record, language, version, or other paid operation, so changing them can change the value of the response even when the payment amount stays the same. Treat headers as part of the request contract too. An endpoint that returns a different representation, or rejects an unsupported header, may require a new call and possibly a new payment.
5. Request JSON output
npx awal@2.12.1 x402 pay <url> --jsonUse --json when another program needs structured output rather than human-oriented terminal text. Keep the payment response or transaction hash with the result so you can reconcile what the client paid against the response it received.
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What happens between the first request and the paid response?
x402 separates the initial request from the paid retry. The service provides its terms first; the client signs and presents proof only after it can evaluate the request.
- The client requests the endpoint. It sends the intended URL, method, query values, and any required headers or body.
- The server returns a challenge. The response is
402 Payment Requiredand includes machine-readable payment requirements. - The wallet signs locally. The client uses the challenge to prepare a USDC payment authorization. The wallet signs it; it does not send the private key to the seller.
- The client retries with payment proof. It encodes the proof in the payment header and submits the request again.
- The payment is verified and settled. The server or facilitator verifies and settles the payment on-chain, then returns the requested data along with a settlement response header.
The order matters: the challenge is where the endpoint specifies the exact payment terms. Base USDC is a primary example in the cited materials, but supported networks and assets can change. Follow the live challenge rather than hard-coding a network or assuming that a familiar USDC balance is usable for every request.
What is in the payment requirement?
At minimum, the client needs enough information to identify the amount, token, chain, payee, and settlement path. The recipient and facilitator are separate details worth checking: a facilitator can verify and submit a payment while the recipient is the party meant to receive the funds. The challenge is transaction-specific, so copy terms from the live response rather than from an old tutorial or a listing page.
Why local signing matters
The buyer runtime should hold the signing key and produce the authorization locally. The service needs to verify the signed payment, not obtain the private key. Use a wallet funded only for the spending you intend, protect its secret material, and avoid pasting keys into shell history, prompts, tickets, or third-party dashboards. A payment header is proof for the request; it is not a replacement for key security.
How much does an x402 call cost?
The primary quoted cost is the USDC amount in the challenge. The CLI’s maximum is expressed in atomic units, so a six-decimal USDC convention makes 10,000 units equal to $0.01, 50,000 equal to $0.05, 100,000 equal to $0.10, and 1,000,000 equal to $1.00 in the documented examples. Always verify the asset and unit in the live requirement before converting mentally.
Your operational cost can also include the network and settlement conditions associated with the request. The cited command examples do not establish a universal fee schedule or a guaranteed settlement time, and supported networks can evolve. Do not advertise a fixed total cost unless the endpoint and current wallet flow state it explicitly. The safe budgeting rule is to fund the wallet for the quoted USDC plus whatever transaction resources the selected network and wallet require.
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Compare price on a per-request basis, not only by headline cents. A cheaper endpoint that returns incomplete data, requires repeated retries, or has no remedy for a failed result may be more expensive in practice than a higher-priced service that consistently returns usable output.
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How should you find and evaluate an x402 service or bounty?
If you do not already know the endpoint, a machine-readable catalog such as the402 can help you discover services. Its listings include service metadata, provider trust verdicts, purchase records, and owner-set purchasing rules. Treat a listing as a lead, not as authorization to pay: inspect the endpoint’s current 402 requirements before signing.
A bounty-board style listing may tell an agent what service exists and how an owner wants purchases constrained, but the live endpoint remains decisive. A stale listing can point to a changed amount, network, method, or URL. Check that the domain, recipient, and requested operation align with the listing before allowing funds to move.
Compare services using the terms and evidence that affect the transaction and result:
- Price and unit: check the requested amount and whether it is expressed in the expected USDC units.
- Network and token: confirm the challenge’s chain and token details match what your wallet can use.
- Recipient and facilitator: inspect the specified payee and facilitator rather than assuming they are the same across services.
- Trust evidence: consider available provider verdicts and purchase records, while recognizing that a catalog entry is not a guarantee of a good response.
- Refunds and disputes: find out what remedy, if any, the provider offers. An executed x402 push payment is irreversible; a refund requires a separate transfer or a business-logic process.
- Request and response fit: verify that the endpoint supports your HTTP method and payload, and consider whether its output is suitable for your use.
- Operational continuity: note whether the endpoint’s documentation explains errors, response formats, and how to contact the provider when a paid call fails.
There is no universal success-rate statistic or independent market-size figure established in the cited materials. A trust label or transaction record can inform a decision, but it should not be treated as a substitute for checking terms or validating the returned data.
What can an API provider do to accept x402 payments?
A provider can integrate x402 middleware, publish an x402-enabled URL for agent discovery, and receive settled USDC. For receiving and managing agent payments, Coinbase Business describes a receiving account with reconciliation, withdrawal, and holding functions. Eligibility, geographic availability, rates, and terms depend on current provider conditions, so a business should verify them before relying on that setup.
For an API operator, x402 changes how a buyer reaches a paid endpoint; it does not by itself settle questions about service quality, refund policy, or customer support. Publish clear method and payload requirements, make the payment challenge precise, and explain how a buyer can handle a disputed or unsatisfactory result.
Providers should also make discovery data match the live endpoint. If a catalog advertises one amount or network while the 402 challenge requests another, agents may stop or treat the service as unreliable. A clear receipt or settlement response helps buyers reconcile calls, while a documented refund process gives them a path when the protocol’s push payment cannot simply be charged back.
What can go wrong with an x402 payment?
Most avoidable mistakes happen before signing: misreading the amount, assuming the wrong network, or paying an unfamiliar endpoint without checking its terms. Use the challenge as the transaction-specific source of truth and stop if it does not match the request you intend to make.
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The requested amount exceeds your limit
Do not raise the cap automatically. Check the amount and its unit, compare it with the value of the request, and retry only if the higher maximum is intentional. A maximum is a guardrail, not a price estimate.
The wallet cannot satisfy the challenge
Check the live requirement’s network and token against the wallet’s available assets and signing support. Do not substitute a different network or token based on the assumption that all USDC is interchangeable for the request.
The endpoint returns a payment challenge you did not expect
Pause before signing. Verify the URL and inspect the amount, recipient, network, and facilitator in the challenge. If those terms are not clear or do not fit your request, do not proceed.
The endpoint rejects the method or payload
Payment does not make an unsupported request valid. Confirm whether the service expects GET or POST, which fields are required, and which headers it accepts. If you paid for a request that was malformed, the protocol does not automatically reverse the transfer.
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The payment succeeds but the result is missing or unusable
Retain the payment response or transaction hash, along with the request details and returned headers, for reconciliation. Since an executed payment is not reversed automatically, contact the provider through its stated process or rely on any separately defined refund or dispute mechanism.
The catalog and endpoint disagree
Do not rely on the catalog’s older amount, network, or provider information. Re-read the live 402 challenge and compare the domain and recipient with the service you intended to call. If the discrepancy cannot be explained, stop and choose another provider.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical pre-signing checklist
- Confirm the URL, HTTP method, query, headers, and body.
- Read the 402 response and record amount, unit, token, network, recipient, and facilitator.
- Compare the quote with the value of the requested data or computation.
- Set
--max-amountin atomic units before the wallet signs. - Verify that the wallet has the required USDC and supports the specified network.
- Sign locally; never disclose the private key to the provider.
- After settlement, save the response, settlement header, and transaction hash with the request record.
- Validate the returned data before using it in a consequential workflow.
What should you remember before authorizing payment?
- Payment without an account is possible, but signing still requires a funded wallet.
- Read the endpoint’s current challenge for the chain, token, amount, recipient, and facilitator.
- Set the CLI’s maximum amount before signing and understand that its value is in USDC atomic units.
- Keep a receipt, and assess the provider and expected response before making an irreversible payment.
- Use catalogs for discovery, not as a substitute for inspecting the live endpoint.
Frequently Asked Questions
Can I use x402 to pay any API that returns HTTP 402?
No. A status code alone does not mean an endpoint implements the x402 payment flow or provides a compatible challenge. Use a service that exposes x402 payment requirements and confirm the client can handle its request format.
Do I need an API key, subscription, or merchant account?
Not for the x402 payment flow described here. You need a funded signing wallet, a compatible client, and an endpoint that returns x402 requirements. A provider may still maintain its own operational records or policies.
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Not necessarily. The wallet must support the token and network specified by the live challenge and be able to sign the required authorization. USDC on one network should not be assumed to satisfy a request on another.
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What does –max-amount 10000 mean?
The documented CLI uses USDC atomic units. In its examples, 10,000 units equals $0.01, so the option caps the payment at one cent when the requested asset uses that unit convention.
Is an x402 payment refundable if the response is wrong?
The payment is an exact push payment and is irreversible once executed through the protocol. A refund would require a separate transfer or the provider’s own business-logic or dispute process.
Does x402 guarantee that an AI agent’s answer is accurate?
No. x402 handles payment authorization and settlement, not the truth or usefulness of a service’s output. Validate important results independently, especially when a paid response will drive consequential actions.
What should I save after a paid request?
Keep the request details, payment response or transaction hash, settlement response header, and returned data. These records let you reconcile the amount paid and provide evidence if you need to contact the provider.
Is there a published x402 success rate or market-size figure?
The cited official materials do not establish a universal success-rate statistic or an independent market-size figure. Do not infer either from service listings, purchase records, or a provider’s own trust information.
Can a merchant automatically reverse an x402 payment if a request fails?
The cited material describes an executed push payment as irreversible, rather than a payment that can be charged back through the protocol. Any refund would need a separate transfer or a provider’s own business process.
How can a provider start receiving payments?
A provider can integrate x402 middleware, publish an x402-enabled URL for discovery, and use receiving infrastructure such as a Coinbase Business account where eligible. Current availability, geography, rates, and terms should be verified directly.
The Bottom Line
x402 lets an agent pay per request in USDC by reading an HTTP 402 challenge, signing locally, and retrying with payment proof. Use the five documented CLI forms, cap spending in atomic units, verify the live network and recipient, and remember that settlement is not a guarantee of service quality or a built-in refund.
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