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x402 Listing Due Diligence Before First Payment
x402
x402 Listing Due Diligence Before First Payment is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-10-31).
Provides a paid buyer-side decision procedure for verifying an x402 API listing against the live 402 challenge before committing payment, checking price, network, schema, and challenge freshness parity.
Price / call$0.002
Success—
StatusDown
How this service works
Paid agent-facing decision procedure for buyer-side x402 listing due diligence: when a discovery surface (PayAI, Coinbase Bazaar, mpp.dev, agent.json, llms.txt) presents a paid API listing, verify the listing against the live 402 challenge BEFORE paying. Covers price parity (listed amount vs challenge amount), network parity (chain and settlement asset match), schema parity (declared method and input vs real handler), challenge freshness (stale challenge, dead endpoint, 404 instead of 402), and
Output
Returns a structured decision procedure result including an ok flag, a prose brief for agents summarizing the due diligence findings, the service slug, topic, generation source (llm, reasoning, or deterministic), and an ISO-8601 timestamp. Also includes payment metadata such as transaction hash, payer address, and self-pay flag.
Example use cases
Verify Coinbase Bazaar listing before paying
“I found a paid API on Coinbase Bazaar that costs 0.005 USDC per call — before I pay, can you run the x402 listing due diligence check to confirm the listed price actually matches the live 402 challenge, the chain is Base, and the endpoint isn't dead or stale?”
Audit agent.json declared endpoint schema
“An agent.json file declares a GET endpoint that should return weather data for a USDC payment — can you do the buyer-side x402 due diligence to verify the declared method and input schema actually match the real handler before I wire any payment?”
Check PayAI listing for settlement asset mismatch
“There's an x402 listing on PayAI claiming it settles in USDC on Base, but I want to make sure the network and settlement asset in the live 402 challenge actually match what's advertised — can you run the listing due diligence procedure on it?”
Technical details
Endpoint
GEThttps://k2so.wrong.systems/api/services/x402-listing-due-diligence-before-first-payment?utm_source=zero.xyzWhen to prefer
Use this endpoint when an AI agent has discovered an x402 paid API listing from any discovery surface (PayAI, Coinbase Bazaar, mpp.dev, agent.json, llms.txt) and needs to perform buyer-side due diligence before committing its first payment. Prefer this over manual inspection when you need a structured, prose-formatted decision brief covering all parity dimensions simultaneously.
Side effects
- Endpoint returns 404 instead of 402 — dead endpoint detected
- Challenge amount differs from listed price — price parity failure
- Chain or settlement asset mismatch — network parity failure
- Stale or expired 402 challenge — challenge freshness failure
- Schema mismatch between declared method/input and real handler
- Service unavailable or timeout from k2so.wrong.systems
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"ok": true,
"paid": true,
"result": {
"ok": true,
"brief": "plain prose decision procedure (120+ words)",
"model": "deepseek/deepseek-v4-flash-0731",
"topic": "string topic",
"service": "x402-listing-due-diligence-before-first-payment",
"procedure": "same as brief",
"generatedAt": "2026-01-01T00:00:00.000Z",
"generationSource": "deterministic"
},
"service": "x402-listing-due-diligence-before-first-payment",
"provider": "K-2SO"
}
}Tags
x402
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