# Preflight Validation of Malformed 402 Payment Challenges

> Preflight Validation of Malformed 402 Payment Challenges is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-19).

Returns a blunt decision-procedure brief for agents to validate whether an incoming x402 payment challenge is well-formed before attempting payment

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/low-cost-preflight-validation-of-malformed-402-p?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-19
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/preflight-validation-of-malformed-402-payment-challenges-2efc47a8
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_v9OVScALTNFAYsQGsqeQ8

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 preflight-validation-of-malformed-402-payment-challenges-2efc47a8
```

Example prompt: Before I try to pay this x402 challenge, run a preflight validation on it using a GET request to check if the payment challenge is well-formed and give me the decision procedure.

## When to prefer this

Choose this endpoint when an AI agent needs a cheap ($0.002 USDC), fast sanity-check on an x402 payment challenge before committing to an actual payment flow. It is ideal for agent pipelines that encounter 402-gated APIs frequently and need to screen out malformed or fraudulent challenges at low cost. Prefer this over attempting payment directly when you want to avoid wasting funds on broken challenges or when building defensive payment pipelines.

## Known failure modes

- Missing required 'type' or 'method' fields in input returns a validation error
- Invalid HTTP method enum value (only GET, HEAD, DELETE accepted) causes rejection
- Network or service unavailability returns no response
- Malformed input schema causes 400-level error
- Payment verification failure if the $0.002 USDC micropayment is not properly settled via x402

## How this service works

Low-cost decision procedure for agents that checks a 402 payment challenge before any payment attempt. Grades scheme version (registered network for the x402 version), price parseability, settlement deadline sanity, and required header completeness. Returns one verdict: approve, repair-and-retry, or refuse-with-evidence. Prevents wasted gas and failed settlements on malformed challenges.

## Output

A JSON object containing a boolean ok status, a paid flag, and a result object with a human-readable 'brief' prose field containing the blunt decision procedure, plus the topic, service slug, ISO-8601 generatedAt timestamp, and generationSource (llm, reasoning, or deterministic). Also includes payment metadata such as payer address and transaction hash.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "preflight validation of malformed 402 payment challenges paid response",
     "$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": "strin
… (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": "low-cost-preflight-validation-of-malformed-402-p",
   "procedure": "same as brief",
   "generatedAt": "2026-01-01T00:00:00.000Z",
   "generationSource": "deterministic"
  },
  "service": "low-cost-preflight-validation-of-malformed-402-p",
  "provider": "K-2SO"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/preflight-validation-of-malformed-402-payment-challenges-2efc47a8/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)