# x402 Multi-Rail Settlement Selection Standard

> x402 Multi-Rail Settlement Selection Standard 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 2026-10-20).

Returns a decision procedure for agents choosing between Solana and Base settlement rails when an HTTP 402 challenge offers multiple payment options.

## Facts

- Endpoint: GET https://k2so-8080.on.ascii.dev/api/services/x402-multi-rail-settlement-selection-when-an-age?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-20
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-multi-rail-settlement-selection-standard-07f0935e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Wk0-HUreNtyJCMtbPogxf

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 x402-multi-rail-settlement-selection-standard-07f0935e
```

Example prompt: I just received an HTTP 402 challenge that offers both Solana and Base as settlement rails — walk me through the decision procedure for picking the right one, including fee thresholds, latency considerations, and what to do if one rail's facilitator is down.

## When to prefer this

Use this endpoint when your agent encounters an HTTP 402 challenge that presents multiple blockchain settlement rails (specifically Solana and Base) and needs a structured, authoritative decision procedure rather than ad-hoc logic. Prefer this over general x402 documentation when you need per-rail fee thresholds, latency comparisons, facilitator fallback sequences, and session lifecycle rules consolidated into a single actionable brief. It is especially valuable for autonomous agents that must make rail selection decisions programmatically without human oversight.

## Known failure modes

- Payment not provided — endpoint requires $0.002 USDC per call via x402; unpaid requests return 402 challenge
- Invalid method — only GET, HEAD, DELETE are accepted; POST/PUT will be rejected
- Facilitator unavailable — if the backend generation service is down, no procedure is returned
- Malformed input object — missing required 'type' or 'method' fields returns validation error
- Rate limiting — excessive calls may be throttled by the provider

## How this service works

Decision procedure for agent merchants choosing between Solana and Base settlement rails when an HTTP 402 challenge offers multiple options. Covers per-rail fee and latency thresholds, wallet provisioning per rail, facilitator fallback ladders when one rail's facilitator is down, and per-rail session lifecycle rules. Blunt procedure, not marketing.

## Output

A structured response containing decision procedure prose (the 'brief' field) covering: per-rail fee and latency thresholds for choosing between Solana and Base, wallet provisioning requirements per rail, facilitator fallback ladders when one rail is unavailable, and per-rail session lifecycle rules. Also includes metadata like model used, generation source (llm/reasoning/deterministic), ISO-8601 timestamp, and service slug.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "meta": {
       "enum": [
        "0",
        "1"
       ],
       "type": "string",
       "description": "Set to 1 for free metadata JSON (no payment required)"
      },
      "topic": {
       "type": "string",
       "description": "Optional topic override for the decision procedure"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "title": "x402 multi-rail settlement selection standard paid response",
     "$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": "string"
        
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-multi-rail-settlement-selection-standard-07f0935e/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)