# Multi-rail x402 Payment Flow Protocol Classification Procedure

> Multi-rail x402 Payment Flow Protocol Classification Procedure is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-10-16).

Returns a decision procedure for identifying which x402 payment flow protocol an unfamiliar paid endpoint speaks and what steps are required to pay it

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/multi-rail-x402-payment-flow-protocol-classifica?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-10-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/multi-rail-x402-payment-flow-protocol-classification-procedure-a347d534
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_FJkN2yZulbK7fpdDQ7CnS

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 multi-rail-x402-payment-flow-protocol-classification-procedure-a347d534
```

Example prompt: I just hit an unfamiliar paid endpoint that returned a 402 and I need to figure out which x402 payment flow it speaks — Base challenge, Solana CIRC Token-2022, MPP Tempo, or gateway wrapper — and what steps I need to take before I can pay it. Can you get me the decision procedure for classifying multi-rail x402 payment flows?

## When to prefer this

Use this endpoint when an AI agent encounters an unfamiliar paid endpoint returning a 402 and needs to programmatically determine which x402 payment flow protocol it implements before attempting payment. Prefer this over generic documentation searches when you need a blunt, agent-executable decision procedure specifically covering Base x402 challenge, Solana CIRC Token-2022, MPP Tempo challenge, and gateway wrapper flows in a single authoritative brief.

## Known failure modes

- Payment not completed — endpoint returns 402 challenge requiring $0.002 USDC before content is delivered
- Invalid method — only GET/HEAD/DELETE accepted
- Upstream LLM generation failure — result.ok may be false with no brief returned
- Topic override produces out-of-scope result if topic param is unrelated to x402 flows

## How this service works

Decision procedure for an agent that hits an unfamiliar paid endpoint and must identify which payment flow it speaks before paying. Classifies Base x402 challenge (WWW-Authenticate Payment, eip155: 8453, USDC), Solana CIRC Token-2022 quote-transfer-resend flow, MPP Tempo gateway challenge, and gateway-wrapper endpoints (which hide a flow behind another host). Returns protocol id, required headers, token/network, resend semantics, single-use flag, and the exact ordered steps to settle. Includes

## Output

A structured JSON response containing a prose decision procedure (brief field) describing how to classify x402 payment flow protocols across rails (Base x402 challenge, Solana CIRC Token-2022 quote-transfer-resend, MPP Tempo challenge, gateway wrapper), along with the topic, service slug, generation source (llm/reasoning/deterministic), and ISO-8601 timestamp of generation.

## Request schema (JSON Schema)

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

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/multi-rail-x402-payment-flow-protocol-classification-procedure-a347d534/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)