# 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-8080.on.ascii.dev, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-13).

Returns a deterministic decision procedure for merchants to safely validate and inspect incoming paid API request payloads before executing them in an x402-gated service on Base.

## Facts

- Endpoint: GET https://k2so-8080.on.ascii.dev/api/services/agent-infrastructure-decision-procedures-for-x40
- 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/merchant-side-x402-pre-flight-payload-inspection-procedure-bc18e2ad
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_N-9QVkm1UVv0ojiu8tckS

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-bc18e2ad
```

Example prompt: I'm wrapping my API as an x402 service on Base — can you get me the merchant-side pre-flight payload inspection procedure so I know how to safely validate incoming paid request payloads for injection attacks, size limits, and schema conformance before I execute them?

## When to prefer this

Choose this endpoint when you are building or operating an x402 merchant service on Base and need authoritative, structured guidance on pre-execution payload inspection — particularly for injection defense, schema enforcement, size/depth limiting, and path-traversal prevention. Prefer this over generic security checklists when you need x402-specific, agent-readable procedure briefs that can be directly consumed by an autonomous merchant agent.

## Known failure modes

- Invalid or missing HTTP method enum value returns a schema validation error
- Non-GET/HEAD/DELETE method not supported by this endpoint
- Malformed query parameters (e.g. meta not '0' or '1') may return an error or default behavior
- Service unavailability on the provider host returns a network error with no procedure
- Payment not completed results in a 402 response without the decision procedure content

## 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 decision procedure brief for the merchant, including a prose description of the validation steps, an ok/success flag, the service slug, generation source (llm, reasoning, or deterministic), an ISO-8601 timestamp, and optional model/topic metadata — all indicating whether the procedure was successfully retrieved and what logic to apply.

## 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)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/merchant-side-x402-pre-flight-payload-inspection-procedure-bc18e2ad/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from k2so-8080.on.ascii.dev](https://www.zero.xyz/host/k2so-8080.on.ascii.dev/llms.txt)