# X402 Challenge Version Check

> X402 Challenge Version Check is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-13).

Validates whether a given x402 challenge protocol version is supported by comparing it against a caller-supplied list of accepted versions, returning acceptance status and mismatch reasons.

## Facts

- Endpoint: POST https://api.delx.ai/api/v1/x402/x402-challenge-version-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/x402-challenge-version-check-3398636b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_2faeU0w-Tu5mYFQv1cbBd

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-challenge-version-check-3398636b -d '<json body>'
```

Example prompt: Before I accept this x402 payment challenge, check if version 3 is compatible with our supported versions [1, 2, 3, 5] and tell me whether to accept or reject it.

## When to prefer this

Use this endpoint when an agent or service needs a deterministic, auditable check of whether an incoming x402 challenge version is permissible before proceeding with payment or accepting a delivery. Prefer this over manual in-code comparisons when you need normalized evidence and explicit rejection reasons logged for audit trails, or when building payment-gating workflows where version mismatches must be surfaced clearly.

## Known failure modes

- Version integer outside expected range returns rejection with mismatch details
- supported_versions array exceeds 256-item limit returns validation error
- Missing required version or supported_versions fields returns 400 bad request
- Empty supported_versions list always results in rejection
- Non-integer version values cause schema validation failure

## How this service works

X402 Challenge Version Check: X402 Challenge Version Check compares challenge protocol version with supported versions from bounded caller-supplied values without an external provider. Call X402 Challenge Version Check before paying for or accepting an x402 or agent delivery assembled from caller-supplied challenge and result metadata. Returns contract-specific checks, normalized evidence, mismatch reasons, and an explicit acceptance or rejection status for X402 Challenge Version Check as versi…

## Output

Returns an explicit acceptance or rejection status for the given x402 challenge version, along with contract-specific check results, normalized evidence, and detailed mismatch reasons explaining why the version was or was not accepted.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "version": {
   "type": "integer",
   "description": "Version supplied to X402 Challenge Version Check; used only for this bounded calculation and processed in memory without retention."
  },
  "supported_versions": {
   "type": "array",
   "items": {
    "type": "integer"
   },
   "maxItems": 256,
   "description": "Supported Versions supplied to X402 Challenge Version Check; used only for this bounded calculation and processed in memory without retention."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "result": {
   "version": 2,
   "supported": true,
   "supported_versions": [
    1,
    2
   ]
  },
  "schema": "delx/util-x402-challenge-version-check/v1",
  "status": "pass",
  "evidence": {
   "retained": false,
   "input_sha256": "19a97d5b88dfc156ec9b3f1ff4cfb324dd9d18bb96d5ff480a3478193db0eeab",
   "external_calls": 0
  },
  "operation": "delivery_contract:x402_challenge_version_check"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/x402-challenge-version-check-3398636b/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.delx.ai](https://www.zero.xyz/host/api.delx.ai/llms.txt)