# Pre-payment Rail-Selection Decision Procedure for x402 Agents

> Pre-payment Rail-Selection Decision Procedure for x402 Agents is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-10-31).

Returns a blunt, LLM-generated decision procedure brief telling an AI agent which payment rail (Base, Solana, Polygon, Arbitrum, Avalanche, gasless Solana) to use before executing an x402 payment.

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/pre-payment-rail-selection-decision-procedure-fo?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-10-31
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pre-payment-rail-selection-decision-procedure-for-x402-agents-1b0b0dea
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_9ier8aLRgnUjr11WMsMx1

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 pre-payment-rail-selection-decision-procedure-for-x402-agents-1b0b0dea
```

Example prompt: Before I pay this x402 invoice, give me the blunt decision procedure for picking which rail to use — I'm facing a multi-network 402 challenge and need to choose between Base, Solana, Polygon, Arbitrum, Avalanche, or gasless Solana.

## When to prefer this

Use this endpoint when an AI agent is about to execute an x402 payment and needs to decide which blockchain rail to use before committing funds — especially when multiple network challenges are present simultaneously (Base, Solana, Polygon, Arbitrum, Avalanche, gasless Solana). Prefer this over generic documentation when you need a blunt, agent-optimized decision procedure rather than marketing material.

## Known failure modes

- Missing or invalid payment header results in a 402 response requiring USDC payment before content is returned
- Invalid query parameter values (e.g. unsupported meta enum) may result in a 400 error
- LLM generation failure may produce an ok:false result in the response body
- Network or provider downtime could yield a 5xx error with no brief returned

## How this service works

Paid agent-facing brief on Pre-payment rail-selection decision procedure for x402 agents facing multi-network 402 challenges (Base, Solana, Polygon, Arbitrum, Avalanche, gasless Solana): how to pick which rail to pay on before funds move-0. Blunt decision procedure, not marketing.

## Output

A prose decision-procedure brief telling the agent exactly how to select a payment rail before funds move, including the topic covered, generation source (llm, reasoning, or deterministic), ISO-8601 timestamp, and service slug. The 'procedure' and 'brief' fields contain the actionable guidance.

## Request schema (JSON Schema)

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

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pre-payment-rail-selection-decision-procedure-for-x402-agents-1b0b0dea/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)