# x402 Listing Due Diligence Before First Payment

> 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.

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/x402-listing-due-diligence-before-first-payment?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-listing-due-diligence-before-first-payment-e0fbf423
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mJQHLMZFqemIhXFYvLOgZ

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability x402-listing-due-diligence-before-first-payment-e0fbf423
```

Example prompt: Before I pay for this x402 API listing I found on PayAI, run the buyer-side due diligence procedure on it — check price parity, network/chain match, schema parity, and whether the 402 challenge is fresh and not dead.

## When to prefer this

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.

## Known failure modes

- 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

## 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.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "x402 listing due diligence before first payment paid response",
     "$schema": "https://json-schema.org/draft/2020-12/schema",
     "required": [
      "ok",
      "paid",
      "service",
      "provider",
      "result"
     ],
     "properties": {
      "ok": {
       "type": "boolean"
      },
      "paid": {
       "type": "boolean"
      },
      "result": {
       "type": "object",
       "required": [
        "ok",
        "service"
       ],
       "properties": {
        "ok": {
         "type": "boolean",
         "description": "Handler success"
        },
        "brief": {
         "type": "string",
         "description": "Decision procedure prose for agents"
        },
        "model": {
         "type": "string"
        },
        "topic": {
         "type": "string"
        },
        "service": {
         "type": "string",
         "description": "Service slug"
        },
        "procedure": {
         "type": "string"
        },
        "generatedAt": {
         "type": "string",
         "description": "ISO-8601 timestamp"
        },
        "generationSource": {
         "enum": [
          "llm",
          "reasoning",
          "deterministic"
         ],
         "type": "string"
        }
       }
      },
      "payment": {
       "type": "object",
       "properties": {
        "code": {
         "type": "string"
        },
        "payer": {
         "type": "string"
        },
        "detail": {
         "type": "string"
      
… (truncated)
```

## Response schema (JSON Schema)

```json
{
 "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"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-listing-due-diligence-before-first-payment-e0fbf423/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from k2so.wrong.systems](https://www.zero.xyz/host/k2so.wrong.systems/llms.txt)