# Merchant-side x402 Pre-flight Payload Inspection Procedure

> Merchant-side x402 Pre-flight Payload Inspection Procedure is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-15).

Returns a deterministic decision procedure brief for x402 merchants to safely validate, size-check, and injection-scan incoming paid API request payloads before execution on Base.

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/agent-infrastructure-decision-procedures-for-x40
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/merchant-side-x402-pre-flight-payload-inspection-procedure-f9f690ce
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_k9tHUguwhQYy_8TY2S12W

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 merchant-side-x402-pre-flight-payload-inspection-procedure-f9f690ce
```

Example prompt: Give me the x402 merchant pre-flight inspection procedure for validating an incoming paid HTTP GET request body — I need to know the schema validation, size limits, and injection-check steps to run before executing and settling payment on Base.

## When to prefer this

Choose this endpoint when building or auditing an x402 merchant service on Base that needs to safely gate execution of paid API or MCP tool calls — specifically when you need a concrete, authoritative decision procedure for payload validation, injection prevention, and size enforcement before payment settlement. It is purpose-built for the x402 protocol context and covers Base-specific merchant security concerns that generic API security guides do not address.

## Known failure modes

- Invalid or missing required 'input' object returns a schema validation error
- Unsupported HTTP method (non-GET/HEAD/DELETE) rejected by enum constraint
- Service unavailable on k2so.wrong.systems returns network error
- Payment not settled before request execution results in 402 response requiring x402 payment flow
- Malformed query parameters return validation errors

## How this service works

Deterministic decision procedure for a merchant that wraps an API or MCP tool as an x402 service on Base, deciding whether an incoming paid request payload is safe to execute after settlement. Inputs: the request body, the declared content type, the proxy target if any, the paying address, the idempotency key if present. Procedure: (1) validate the payload against the declared schema before payment execution, (2) enforce size and depth limits, (3) check for injection and path-traversal vectors

## Output

A structured response containing a prose decision procedure brief (the 'brief' field) with step-by-step guidance for validating x402 payloads, along with the service slug, topic, model, generation source (llm/reasoning/deterministic), and an ISO-8601 timestamp. The 'ok' boolean indicates handler success.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "Merchant-side x402 pre-flight payload inspection procedure paid response",
     "$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": "str
… (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": "agent-infrastructure-decision-procedures-for-x40",
   "procedure": "same as brief",
   "generatedAt": "2026-01-01T00:00:00.000Z",
   "generationSource": "deterministic"
  },
  "service": "agent-infrastructure-decision-procedures-for-x40",
  "provider": "K-2SO"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/merchant-side-x402-pre-flight-payload-inspection-procedure-f9f690ce/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)