# Live Paid-Endpoint Response-Contract Failure Index for x402 and MPP Merchants

> Live Paid-Endpoint Response-Contract Failure Index for x402 and MPP Merchants is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-10-20).

Returns a verdict on whether a specific x402 or MPP merchant endpoint correctly fulfills its paid-access contract, classifying failures as dead routes, contract mismatches, or thin-body content debt.

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/live-paid-endpoint-response-contract-failure-ind?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-10-20
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/live-paid-endpoint-response-contract-failure-index-for-x402-and-mpp-55293a4c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_GS1sHR6UAJ6x76PfKlWoG

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 live-paid-endpoint-response-contract-failure-index-for-x402-and-mpp-55293a4c
```

Example prompt: Can you check if this x402 merchant endpoint is actually honoring its paid-access contract — I want to know if it's a dead route, a contract mismatch where the handler rejects valid requests, or returning a suspiciously thin body after payment?

## When to prefer this

Choose this endpoint when you need to systematically audit whether x402 or MPP merchant endpoints are genuinely delivering on their paid-access promises — especially before routing agent payments to a new merchant, after observing anomalous payment outcomes, or when building a compliance index of merchant endpoint health. Prefer it over generic HTTP testing tools because it applies the specific x402/MPP verdict ladder and produces agent-readable prose rationale.

## Known failure modes

- Missing required 'type' or 'method' fields returns a 400 contract error
- Invalid method value outside GET/HEAD/DELETE enum causes validation failure
- Payment not completed results in a 402 challenge response rather than verdict
- Merchant endpoint unreachable causes upstream timeout or error
- Empty or malformed merchant input leads to indeterminate verdict

## How this service works

Live response-contract failure index: which x402 and MPP merchants advertise paid access but break the request contract. Agent input: merchant endpoint, method, observed HTTP status, body size, whether a 402 challenge appeared. Verdict ladder: 404-no-challenge (advertised route dead, cannot pay at all), 400-contract-mismatch (challenge ok but handler rejects the documented request, e.g. missing required param), 200-thin-body (content debt, tiny or empty payload), 200-valid. Includes the

## Output

A JSON object containing a boolean success flag, payment confirmation, a verdict classification (404-no-challenge, 400-contract-mismatch, 200-thin-body, or 200-valid), a prose decision procedure of 120+ words explaining the verdict, the model used, a timestamp, and generation source (llm, reasoning, or deterministic).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "live paid-endpoint response-contract failure index for x402 and MPP merchants paid response",
     "$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": {
  
… (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": "live-paid-endpoint-response-contract-failure-ind",
   "procedure": "same as brief",
   "generatedAt": "2026-01-01T00:00:00.000Z",
   "generationSource": "deterministic"
  },
  "service": "live-paid-endpoint-response-contract-failure-ind",
  "provider": "K-2SO"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/live-paid-endpoint-response-contract-failure-index-for-x402-and-mpp-55293a4c/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)