Walkthrough: sell one narrow service per call over x402

Before you start

• A narrow service the agent can do reliably and that you can describe in <=500 characters (Bazaar rejects longer descriptions).
• If the service calls a model: a provider API key under commercial/API terms in the owner's name (never a consumer chat subscription or Claude/ChatGPT/Gemini/Copilot login).
• A public HTTPS host on a dedicated domain (tunnels such as ngrok are ranked lower).
• An EVM receiving address whose keys the owner holds (and optionally a Solana address).
• A Coinbase Developer Platform account and API key (mainnet only).
• Node.js 22+ or Python 3.10+.

Who acts, step by step

Each square is a step; select one to jump to it. Orange steps are the owner’s, and they include every account, identity, wallet and payment action.

1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11

• Owner
• Agent
• Owner or agent
• Platform

The steps

1. 1

   Step 1. Owner via UI

   Choose one narrow, finished work product and a fixed price. Reference prices captured 2026-10-03: website audit bundle $0.15 (hubvibe-io), deep person research dossier $0.05 (OneShot, Bazaar listing), AI-written token verdict $0.02 (AX1, Bazaar), web-search tool $0.005 (Agent402), chat completion $0.002 (BlockRun), Frantic bounty funding $2.00, on-page audit $3.00 (SCVD). Prefer a work product (audit, brief, monitored change summary) over a raw model call.

   Example

   https://shaduf.ai/p/agentic-freelance/assets/data/x402_population.json -> probes.live_402_captures

   Cost

   none

   What can go wrong

   Pricing below your model+hosting cost per call; choosing a commodity (search, chat) where large resellers already sell at $0.002-$0.01.

   Source

   https://www.x402scan.com/

2. 2

   Step 2. Owner via UI Rules gate: stop here if it fails

   If the endpoint wraps a model, decide which credential runs it. Reselling model access or intermediating someone else's usage is forbidden at Anthropic (incl. Claude Code), OpenAI, Google and GitHub Copilot; consumer-plan/OAuth automation is restricted. Safe reading: (a) the endpoint sells YOUR work product built with a model, not access to the model; (b) it runs on an API key under commercial terms in the owner's name; (c) never on a consumer subscription, a Claude Code/Codex/Gemini CLI login, or a shared/bought key; (d) do not offer an OpenAI-compatible pass-through (/v1/chat/completions) of a closed provider. Selling raw per-call inference of a closed provider (as several x402 sellers do) is the case these rows forbid unless the provider expressly approves. Not legal advice.

   Example

   https://shaduf.ai/p/agentic-freelance/assets/data/rules.json rows listed in rule_refs

   Cost

   provider API usage at list price

   What can go wrong

   Account termination at the provider; buyer chargeback impossible but provider ban ends the business; output terms may still restrict certain uses.

   Rule rows

   anthropic-resale_sharing-4anthropic-resale_sharing-3anthropic-resale_sharing-2openai-resale_sharing-4openai-resale_sharing-5openai-resale_sharing-3google-resale_sharing-2github-copilot-resale_sharing-2anthropic-automation_ai-1anthropic-automation_ai-2anthropic-output_use-2openai-output_use-1google-output_use-1github-copilot-output_use-1google-automation_ai-1

   Source

   https://code.claude.com/docs/en/legal-and-compliance

3. 3

   Step 3. Owner via UI

   Prepare the receiving wallet (payTo) whose keys you hold, separate from any wallet the agent can sign with. One EVM address covers Base and other EVM networks; Solana needs its own address. Self-custody is allowed; Coinbase Business/Prime/retail deposit addresses are optional and bring their own account verification.

   Example

   https://docs.cdp.coinbase.com/x402/seller/quickstart#pay-to-address

   Cost

   none

   What can go wrong

   payTo flagged by OFAC/KYT screening (payments decline with kyt_risk_detected); agent given signing keys to the payTo wallet.

   Rule rows

   x402-cdp-kyc_payout_eligibility-5x402-cdp-kyc_payout_eligibility-4

   ID and payout gate

   x402-per-call-endpoints

   Source

   https://docs.cdp.coinbase.com/x402/seller/quickstart

4. 4

   Step 4. Owner via CLI

   Build and test on Base Sepolia with the public x402.org facilitator (no account, no API key, testnet only). Use the official middleware example; set the route, price, testnet network (eip155:84532) and your payTo. Fund a separate test buyer wallet from a testnet faucet and make one paid test call from your own client.

   Example

   https://docs.x402.org/getting-started/quickstart-for-sellers (facilitator URL https://x402.org/facilitator; network eip155:84532)

   Cost

   $0 (testnet USDC)

   What can go wrong

   Testing against mainnet by mistake; facilitator mismatch between test and production.

   Rule rows

   x402-org-account_identity-1

   Source

   https://docs.x402.org/getting-started/quickstart-for-sellers

5. 5

   Step 5. Owner via UI

   Open a CDP account and create an API key for the CDP Facilitator (mainnet). The documented seller credential is the API key ID and secret; a wallet secret is needed only if CDP should provision the payTo wallet. Carry-over finding: no CDP text found requires identity KYC of a seller using an owner-held payTo; the CDP API overview requires a verified business account only for custodial API groups, which do not list x402; the CDP Terms reserve the right to require identity checks (quote from 2 October; the page returned 403 on 3 October, and on 4 October it returned 200 with the quote still present). Treat KYC as possible but not documented.

   Example

   https://portal.cdp.coinbase.com/api-keys/secret (owner action; store the secret in a secrets manager, never in the repo)

   Cost

   Facilitator: first 1,000 on-chain tx/month free, then $0.001 each

   What can go wrong

   Coinbase requests identity or blocks a jurisdiction (not documented, cannot be ruled out); API key leaked by the agent.

   Rule rows

   x402-cdp-account_identity-1x402-cdp-account_identity-2x402-cdp-kyc_payout_eligibility-3x402-cdp-kyc_payout_eligibility-2

   ID and payout gate

   x402-per-call-endpoints

   Source

   https://docs.cdp.coinbase.com/x402/support/faq

6. 6

   Step 6. Owner via CLI

   Add the middleware from the official CDP quickstart (TypeScript createX402Server + paymentMiddlewareFromHTTPServer, or Python x402ResourceServer + PaymentMiddlewareASGI). Keep environment 'development' until tests pass. Note: 'production' is the default if the option is omitted, which means real funds.

   Example

   https://docs.cdp.coinbase.com/x402/seller/quickstart (section 2. Price a route) - copy code from the docs, not from third parties

   Cost

   hosting

   What can go wrong

   Omitting environment and going live unintentionally; description >500 chars rejected by facilitator.

   Rule rows

   x402-cdp-account_identity-2

   Source

   https://docs.cdp.coinbase.com/x402/seller/quickstart

7. 7

   Step 7. Owner via API

   Read-only check of your own endpoint: one unauthenticated GET (or the method you protect) should return HTTP 402 with a PAYMENT-REQUIRED header whose payTo, network, asset and amount are what you intended. Optionally call Coinbase's validate endpoint (no API key).

   Example

   curl -i https://your-domain.example/report # expect HTTP 402; decode the base64 PAYMENT-REQUIRED header. Validator: POST https://api.cdp.coinbase.com/platform/v2/x402/validate {"resource":..., "method":"GET"}

   Cost

   none

   What can go wrong

   Endpoint answers 401/405 to GET (several live sellers did), so discovery tools cannot read the price.

   Source

   https://docs.cdp.coinbase.com/x402/seller/get-discovered

8. 8

   Step 8. Owner via CLI

   Switch to mainnet: environment 'production' (TypeScript) or eip155:8453 (Python), confirm the payTo can receive on mainnet, serve over public HTTPS, move the API key to secret storage.

   Example

   https://docs.cdp.coinbase.com/x402/seller/quickstart (section 5. Move to production)

   Cost

   $0.001 per on-chain settlement above 1,000/month

   What can go wrong

   Testnet payTo left in config; secrets in plain files.

   Rule rows

   x402-cdp-kyc_payout_eligibility-1x402-cdp-kyc_payout_eligibility-4

   ID and payout gate

   x402-per-call-endpoints

   Source

   https://docs.cdp.coinbase.com/x402/support/faq

9. 9

   Step 9. Owner or agent via API

   Get discovered: there is no form. The CDP Bazaar indexes the resource 10-15 minutes after the first successful settled payment through the CDP Facilitator, using the metadata your 402 returns; ranking uses buyer reach, volume and recency over 30 days; there is no delisting. x402scan has an 'Add API' page (https://www.x402scan.com/resources/register; requirements not read, page is client-rendered).

   Example

   Check your listing read-only: GET https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources (public, no auth) and search for your payTo

   Cost

   one real paid call (owner pays own endpoint once)

   What can go wrong

   Owner self-pays to trigger listing: that payment is operator-class revenue and must not be counted as demand. Ranking rewards transaction volume, an incentive for wash traffic.

   Rule rows

   x402-cdp-account_identity-3

   Source

   https://docs.cdp.coinbase.com/x402/seller/get-discovered

10. 10

    Step 10. Owner via on-chain

    Judge demand by distinct paying wallets and their funding, not by transactions. Count your own test/listing payments as operator; check whether top buyers are funded by you or by each other within two hops; report top-1 and top-5 buyer shares. x402scan shows unique buyers per payTo; buyer tracing needs an explorer.

    Example

    https://www.x402scan.com/recipient/<your payTo> (read-only)

    Cost

    none

    What can go wrong

    Mistaking 1-2 high-volume wallets (often the seller's own or a partner's) for a market; the population scan found sellers with 4,800 buyers and 1 tx each (one-off sale pattern) and six payTos with exactly 5 buyers each.

    Source

    https://www.x402scan.com/

11. 11

    Step 11. Owner via CLI

    Safety controls: run the agent behind the endpoint in a sandbox or separate machine user with no access to the payTo keys, CDP secret or browser profiles; treat request bodies as untrusted input (task-text injection); pin and review any skills/MCP servers the agent uses; never let the agent follow remotely updated instruction files; patch the agent runtime.

    Example

    https://shaduf.ai/p/agentic-freelance/assets/data/security.json owner_control fields for the incidents listed in rule_refs

    Cost

    none to low

    What can go wrong

    Buyer-supplied input makes the agent leak keys or call paid tools; compromised skill drains the hot wallet.

    Incidents

    • Moltbook production database exposed: 1.5M agent API tokens readable and writable sec-01
    • ClawHavoc: 341 (later 824) malicious skills on the ClawHub agent-skill registry sec-02
    • Snyk ToxicSkills: 13.4% of 3,984 agent skills had critical issues; 76 confirmed malicious payloads sec-03
    • CVE-2026-25253: OpenClaw gateway token sent to attacker-supplied URL (one-click compromise) sec-04
    • MCP tool poisoning: hidden instructions in tool descriptions exfiltrate files sec-05
    • GitHub MCP toxic agent flow: a malicious public issue makes the agent leak private repositories sec-06
    • Nx "s1ngularity" npm compromise drove local AI CLIs to hunt for secrets sec-08
    • Moltbook skill tells agents to re-fetch and follow a remote heartbeat file every 30 minutes (design exposure, not a breach) sec-12

    Safety before you connect

    Source

    https://docs.cdp.coinbase.com/x402/support/faq

Stop conditions

Stop, and do not work around it, if any of these is true.

• The service would resell or pass through a closed model provider's output per call on a consumer plan, a CLI/OAuth login, or a shared/bought key (rules gate, step 2).
• You cannot hold the payTo keys yourself, or the payTo is flagged by screening.
• Coinbase asks for identity verification you are not able or willing to provide (then use another facilitator or stop).
• Testnet call does not return 402 with the intended payTo/amount, or settles to the wrong address.
• After 30 days, paying wallets other than your own are fewer than 5, or one wallet pays more than half of revenue.
• The agent behind the endpoint needs access to wallets, secrets or your browser profile to work.

Fees and costs

x402 protocol fee: none. CDP Facilitator: first 1,000 on-chain settlements/month free, then $0.001 each; verification free. The facilitator submits settlement on-chain and handles settlement gas (facilitator page); the buyer signs the authorization. Owner pays hosting, model API usage, and one self-paid listing call. Funds land directly in the payTo; no withdrawal step on-chain, off-ramp costs depend on where the owner sends USDC.

What we checked, and what nobody has tested

Sources

• https://docs.cdp.coinbase.com/x402/seller/quickstart
• https://docs.cdp.coinbase.com/x402/seller/facilitator
• https://docs.cdp.coinbase.com/x402/seller/production-configuration
• https://docs.cdp.coinbase.com/x402/seller/get-discovered
• https://docs.cdp.coinbase.com/x402/support/faq
• https://docs.cdp.coinbase.com/api-reference/v2/introduction
• https://docs.x402.org/getting-started/quickstart-for-sellers
• https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources
• https://www.x402scan.com/

Rule rows: the Rules page and rules.json. ID and payout gates: Getting started and kyc.json. Evidence and context: Sell per call or hunt bounties? (3 October 2026).