# x402 Payment Challenge Verifier

> x402 Payment Challenge Verifier is a paid API for AI agents from agentic-endpoints-testnet.oliver-835.workers.dev, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-12).

Fetches the live x402 payment challenge from a target endpoint and flags any drift in receiving address, network, or asset compared to prior observations

## Facts

- Endpoint: POST https://agentic-endpoints-testnet.oliver-835.workers.dev/x402/verify?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-payment-challenge-verifier-d71b99ae
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_AFxfebPiyKiLdigzhPXAZ

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-payment-challenge-verifier-d71b99ae -d '<json body>'
```

Example prompt: Before I pay that x402 endpoint at https://api.example.com/data, check its live payment challenge and compare it against what the directory says — pay_to address 0xABC123, on the Base network, USDC token — and alert me if anything has drifted.

## When to prefer this

Use this endpoint whenever an AI agent or automated workflow is about to pay an x402-gated API, especially when the endpoint belongs to an unknown or third-party operator. It is the right choice when you want to detect address substitution attacks, verify chain/asset consistency, or enforce a max price cap before committing a payment. Prefer this over blind trust in directory listings when financial safety is a concern.

## Known failure modes

- Private or loopback URLs are refused and not fetched
- Target endpoint is unreachable or returns a non-402 response
- Malformed URL input causes rejection
- No payment challenge returned if the endpoint does not implement x402
- Expected values not provided means no drift comparison is performed

## How this service works

Before paying a stranger's x402 endpoint, read its live payment challenge and compare it against every previous observation. Flags a changed receiving address, network or asset as critical drift. Reports what the endpoint declares; it does not certify the operator.

## Output

Returns the live x402 payment challenge data declared by the target endpoint, along with a drift report comparing it against the expected values you provided. Critical flags are raised for any mismatches in receiving address, network/chain, or asset. The service reports what the endpoint declares without certifying the operator.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "Public HTTP(S) URL of the paid endpoint. Private and loopback addresses are refused, not fetched."
  },
  "expect": {
   "type": "object",
   "properties": {
    "asset": {
     "type": "string",
     "description": "Token contract address"
    },
    "pay_to": {
     "type": "string",
     "description": "Address you expect to pay"
    },
    "network": {
     "type": "string",
     "description": "Chain you expect. A name like 'base' and its CAIP-2 form 'eip155:8453' are treated as the same chain."
    },
    "max_price_usd": {
     "type": "number",
     "description": "Refuse-above threshold in USD"
    }
   },
   "description": "Optional. What you believe to be true, typically from a directory listing. Mismatches are reported so you can trust the live challenge over the listing."
  },
  "method": {
   "type": "string",
   "description": "Method used to provoke the challenge: POST (default), GET or HEAD"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-payment-challenge-verifier-d71b99ae/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentic-endpoints-testnet.oliver-835.workers.dev](https://www.zero.xyz/host/agentic-endpoints-testnet.oliver-835.workers.dev/llms.txt)