# Expired x402 Challenge Re-Probe and Re-Payment Decision Procedure

> Expired x402 Challenge Re-Probe and Re-Payment Decision Procedure is a paid API for AI agents from k2so.wrong.systems, paid per call via x402, $0.002/call, status down (last checked 2026-09-15).

Returns a decision procedure guide for agents handling stale or expired x402 payment challenges, covering expiry detection, safe re-probing, price drift handling, and idempotent re-payment.

## Facts

- Endpoint: GET https://k2so.wrong.systems/api/services/expired-challenge-re-probe-and-re-payment-standa
- Price: $0.002/call
- Payment: x402
- Status: down
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/expired-x402-challenge-re-probe-and-re-payment-decision-procedure-9a3e65ee
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_X-DeOwvIoEem2QcrquJSQ

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 expired-x402-challenge-re-probe-and-re-payment-decision-procedure-9a3e65ee
```

Example prompt: I just got an expired x402 challenge back from a resource I was trying to pay for — can you walk me through the decision procedure for safely re-probing that URL and re-paying without accidentally double-charging myself?

## When to prefer this

Use this endpoint when an AI agent has received an expired or stale x402 challenge and needs a structured, authoritative decision procedure for re-probing and re-paying safely. Prefer this over generic x402 documentation when idempotency, price drift, and nonce binding are concerns in automated agent payment flows. Particularly valuable in long-running autonomous agents where challenges may expire between issuance and settlement.

## Known failure modes

- Endpoint returns an HTTP 402 itself if payment headers are missing or invalid
- Malformed input schema results in a 400 error
- LLM generation failure may return ok:false with an error description in the result
- Price drift beyond agent-configured tolerance may not be handled if topic override is not supplied
- Stale or unavailable upstream LLM may cause generation delay or timeout

## How this service works

Decision procedure for an agent that encounters a stale or expired x402 challenge. Covers expiry detection from WWW-Authenticate headers and cached challenge metadata, safe re-probing of the same resource URL without double-paying, handling price drift between the original challenge and the settlement receipt, and binding the fresh challenge to the original payment intent using a new nonce while preserving idempotency.

## Output

A prose decision procedure brief explaining how an agent should detect x402 challenge expiry from WWW-Authenticate headers or cached metadata, safely re-probe the resource URL without triggering a double payment, handle any price drift between original and fresh challenges, and bind the new nonce to the original payment intent to maintain idempotency. Response includes metadata fields: topic, service slug, model used, generation source, and an ISO-8601 timestamp.

## Request schema (JSON Schema)

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

## 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": "expired-challenge-re-probe-and-re-payment-standa",
   "procedure": "same as brief",
   "generatedAt": "2026-01-01T00:00:00.000Z",
   "generationSource": "deterministic"
  },
  "service": "expired-challenge-re-probe-and-re-payment-standa",
  "provider": "K-2SO"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/expired-x402-challenge-re-probe-and-re-payment-decision-procedure-9a3e65ee/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)