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X402 Payment Replay Key
x402
X402 Payment Replay Key is a paid API for AI agents from api.delx.ai, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-20).
Derives a stable, deterministic replay-detection key from x402 payment metadata (nonce, payer, resource) to prevent duplicate payment attacks.
Price / call$0.001
Success—
StatusUnknown
How this service works
X402 Payment Replay Key: X402 Payment Replay Key derives a stable non-secret replay-detection key from payment metadata from bounded caller-supplied values without an external provider. Call X402 Payment Replay Key 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 Payment Replay Key as versioned dete…
Output
Returns a stable, deterministic replay-detection key derived from the supplied nonce, payer, and resource fields, along with contract-specific validation checks, normalized evidence, any mismatch reasons, and an explicit acceptance or rejection status.
Example use cases
Guard against duplicate payment submissions
“I'm about to accept an x402 payment — can you derive a replay-detection key from nonce 'nonce-9f2a', payer '0x1234abcd...', and resource '/api/v1/report' so I can confirm this payment hasn't already been processed?”
Pre-payment replay check in agent pipeline
“Before my agent pays for a resource, derive a stable replay key from nonce 'abc-001', payer '0xAgent42...', and resource 'https://api.example.com/data' to make sure we're not sending a duplicate transaction.”
Audit trail fingerprinting for x402 payments
“Generate a deterministic replay-detection fingerprint for the x402 payment with nonce 'pay-2024-xyz', payer '0xMerchant99...', and resource '/checkout/item-55' so I can log it and catch any retried payments.”
Technical details
Endpoint
POSThttps://api.delx.ai/api/v1/x402/x402-payment-replay-key?utm_source=zero.xyzWhen to prefer
Use this endpoint when implementing x402 payment acceptance logic and you need a fast, stateless, deterministic replay-detection key computed purely from payment metadata without relying on an external database or provider. Prefer this over building custom hashing logic when you need versioned, contract-aware replay detection that also returns normalized evidence and explicit accept/reject signals.
Side effects
- Missing required fields (nonce, payer, or resource) may return a validation error or incomplete key
- Input values exceeding 8192 character limit per field will be rejected
- Malformed payer address format may produce a mismatch reason in the response
- Network timeout on the POST request returns no key and must be retried
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| nonce | string | Nonce supplied to X402 Payment Replay Key; used only for this bounded calculation and processed in memory without retention. |
| payer | string | Payer supplied to X402 Payment Replay Key; used only for this bounded calculation and processed in memory without retention. |
| resource | string | Resource supplied to X402 Payment Replay Key; used only for this bounded calculation and processed in memory without retention. |
Output
Schema · Response
{
"type": "json",
"example": {
"result": {
"key": "e3cc8d847b2f88337939a2fab5ac3409aebfe27f223855a64805eba4ea53a947",
"fields": [
"nonce",
"payer",
"resource"
],
"secret": false
},
"schema": "delx/util-x402-payment-replay-key/v1",
"status": "pass",
"evidence": {
"retained": false,
"input_sha256": "07fbf5ea1e08edc254770787f1273ba864ab5603eb570e42969f774e980e8a0e",
"external_calls": 0
},
"operation": "delivery_contract:x402_payment_replay_key"
}
}Tags
x402
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