{"uid":"cap_22lLDiiql5w2carW1rcRy","slug":"x402-payment-replay-key-66de6d92","name":"X402 Payment Replay Key","description":"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…","url":"https://api.delx.ai/api/v1/x402/x402-payment-replay-key?utm_source=zero.xyz","method":"POST","headers":{},"bodySchema":{"type":"object","properties":{"nonce":{"type":"string","maxLength":8192,"description":"Nonce supplied to X402 Payment Replay Key; used only for this bounded calculation and processed in memory without retention."},"payer":{"type":"string","maxLength":8192,"description":"Payer supplied to X402 Payment Replay Key; used only for this bounded calculation and processed in memory without retention."},"resource":{"type":"string","maxLength":8192,"description":"Resource supplied to X402 Payment Replay Key; used only for this bounded calculation and processed in memory without retention."}}},"responseSchema":{"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"}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.001","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.001/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_ict7TRscEoXsv_WKn96ra","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.001","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Derives a stable, deterministic replay-detection key from x402 payment metadata (nonce, payer, resource) to prevent duplicate payment attacks.","exampleAgentPrompt":"Before I accept this x402 payment, derive a replay-detection key using nonce '0xabc123', payer '0xDeadBeef...', and resource '/api/v1/premium-data' so I can check for duplicate submissions.","exampleUseCases":[{"title":"Guard against duplicate payment submissions","prompt":"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?"},{"title":"Pre-payment replay check in agent pipeline","prompt":"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."},{"title":"Audit trail fingerprinting for x402 payments","prompt":"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."}],"resultDescription":"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.","failureModes":["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"],"whenToPreferThis":"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.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-20T07:15:25.758Z","isFirstParty":false,"canonicalSlug":"x402-payment-replay-key-66de6d92"}