# K-2SO x402 Merchant Endpoint Pre-Payment Vetting Standard

> K-2SO x402 Merchant Endpoint Pre-Payment Vetting Standard is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-13).

Returns an AI-generated decision procedure (prose brief) for how an agent should assess and vet a paid x402 merchant endpoint before committing payment

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/x402-merchant-endpoint-pre-payment-vetting-stand
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/k-2so-x402-merchant-endpoint-pre-payment-vetting-standard-b36a7c88
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_XtDEocyPZZdsSp1SbxHg0

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 k-2so-x402-merchant-endpoint-pre-payment-vetting-standard-b36a7c88
```

Example prompt: Before I pay for that x402 endpoint, run the pre-payment vetting procedure on it — I want a plain-English decision brief from K-2SO on whether I should proceed with settling the USDC charge.

## When to prefer this

Choose this endpoint when an autonomous agent needs a structured, AI-generated prose brief for deciding whether and how to vet an x402 merchant endpoint before settling USDC payment — especially useful when bootstrapping agent spend-control logic, auditing new x402 merchants, or embedding a reusable decision procedure in an agent's approval workflow. Prefer this over generic LLM prompting when you want a consistent, K-2SO-authoritative vetting standard with structured output and a timestamp.

## Known failure modes

- HTTP 402 returned if payment not yet settled — agent must pay exact USDC amount and retry with PAYMENT-SIGNATURE header
- Invalid method (POST, PUT, PATCH) returns error — only GET/HEAD/DELETE supported
- Malformed queryParams (e.g. invalid 'meta' enum value) may result in 400 error
- Network or upstream LLM failure may return ok:false with empty brief
- Payment signature mismatch or expired payment may cause 402 retry loop

## How this service works

Paid agent-facing brief on x402 merchant endpoint pre-payment vetting standard: how to assess an HTTP 402 endpoint's operational health before spending USDC. Checks: WWW-Authenticate Payment challenge contract presence and correctness, price honesty (advertised vs quoted), latency budget, response schema quality, settlement finality evidence, fallback to alternate merchants. · Build a decision procedure or schema for: x402. Blunt decision procedure, not marketing.

## Output

A JSON object containing: a boolean success flag, a 'paid' confirmation, the service slug, provider name ('K-2SO'), and a result object with a plain-prose 'brief' (120+ words) laying out the decision procedure for pre-payment vetting, plus metadata: the LLM model used, topic, ISO-8601 generation timestamp, and generation source (llm/reasoning/deterministic).

## Request schema (JSON Schema)

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

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/k-2so-x402-merchant-endpoint-pre-payment-vetting-standard-b36a7c88/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)