{"id":"56631f70-e291-4a05-893d-ca174b6147a7","shortId":"xQgTMu","kind":"x402","title":"x402-gated premium API endpoint on Base, pay $0.02 per request in USDC.","tagline":"x402-gated premium API endpoint on Base, pay $0.02 per request in USDC.","description":"This endpoint at `/api/v1/cards/51` is part of the lowpaymentfee.com platform, a collection of x402-protocol pay-per-request APIs spanning data analytics, AI/ML inference, finance/Web3, and infrastructure utilities. The specific `/api/v1/cards/51` resource is labeled \"Premium API Access\" but its exact functionality is not documented beyond that label — it is one of many endpoints on the platform, all priced uniformly at $0.02 per call.\n\nPayment is handled via the x402 protocol on the Base network using USDC (contract `0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`). The challenge advertises a `maxAmountRequired` of 20,000 base units, which at 6 decimals equals $0.02. No API keys or rate limits are required; callers simply attach an `X-PAYMENT` header with a valid x402 payment proof. The endpoint accepts HTTP POST and returns `application/json`.\n\nThe broader platform offers endpoints for metrics, reports, data export, insights, sentiment analysis, text summarization, classification, embeddings, price feeds, exchange rates, token quotes, gas estimates, geocoding, validation, conversion, and generation — all at the same $0.02/request price point. However, documentation beyond the landing page is essentially empty (all sub-pages just show \"Connect wallet\"), so the actual request/response schemas for this and other endpoints are unknown.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","json-api","http-post"],"categories":["api","misc"],"synonyms":["premium API","lowpaymentfee","x402 API","pay-per-call API","Base USDC API","micropayment API"],"warnings":["The exact functionality of /api/v1/cards/51 is undocumented — 'Premium API Access' is the only description available.","All documentation pages (docs, api, pricing, README) return only 'Connect wallet' with no actual content.","No OpenAPI spec, no request schema, and no response schema are available.","The endpoint's purpose must be guessed; it could be a placeholder or test endpoint."],"endpointUrl":"https://lowpaymentfee.com/api/v1/cards/51","protocol":"x402","transport":"http","auth":{"type":"x402","details":[{"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","extra":{"name":"USD Coin","version":"2"},"payTo":"0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3","scheme":"exact","network":"base","mimeType":"application/json","resource":"https://lowpaymentfee.com/api/v1/cards/51","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.300","qualityRationale":"The endpoint is live and returns a valid x402 challenge with clear pricing, but there is no documentation of what this specific endpoint does, no request/response schema, and all doc pages are empty. The 'Premium API Access' label is generic and 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'/request':190 '0.02':10,24,91,124,189 '000':116 '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913':108 '20':115 '6':121 'Base USDC API' 'accept':149 'access':67 'actual':212 'advertis':111 'ai/ml':53 'analysi':167 'analyt':52 'api':5,19,49,66,126 'application/json':154 'attach':135 'base':8,22,103,117 'beyond':75,195 'broader':156 'call':93 'caller':133 'challeng':110 'classif':170 'collect':40 'connect':208 'contract':107 'convers':182 'data':51,163 'decim':122 'document':74,194 'embed':171 'empti':201 'endpoint':6,20,30,83,148,159,219 'equal':123 'essenti':200 'estim':179 'exact':70 'exchang':174 'export':164 'feed':173 'finance/web3':55 'function':71 'gas':178 'gate':3,17 'generat':184 'geocod':180 'handl':96 'header':140 'howev':193 'http':150 'http-post' 'infer':54 'infrastructur':57 'insight':165 'json-api' 'key':127 'label':64,77 'land':197 'limit':130 'lowpaymentfee' 'lowpaymentfee.com':37 'mani':82 'maxamountrequir':113 'metric':161 'micropayment API' 'network':104 'offer':158 'one':80 'page':198,205 'part':34 'pay':9,23,46 'pay-per-call API' 'pay-per-request':45 'payment':94,139,145 'per':11,25,47,92 'platform':38,86,157 'point':192 'post':151 'premium':4,18,65 'premium API' 'price':88,172,191 'proof':146 'protocol':44,100 'quot':177 'rate':129,175 'report':162 'request':12,26,48 'request/response':213 'requir':132 'resourc':62 'return':153 'schema':214 'sentiment':166 'show':207 'simpli':134 'span':50 'specif':60 'sub':204 'sub-pag':203 'summar':169 'text':168 'token':176 'uniform':89 'unit':118 'unknown':221 'usdc':14,28,106 'usdc-base' 'use':105 'util':58 'valid':143,181 'via':97 'wallet':209 'x':138 'x-payment':137 'x402':2,16,43,99,144 'x402 API' 'x402-gated':1,15 'x402-payment' 'x402-protocol':42","prices":[{"id":"52852315-f7c9-4ada-8571-969a3943b6b8","listingId":"56631f70-e291-4a05-893d-ca174b6147a7","amountUsd":null,"unit":"per_call","nativeCurrency":"USD COIN","nativeAmount":"20000","chain":"base","payTo":"0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3","paymentMethod":"x402-usd coin","isPrimary":true,"details":{"scheme":"exact","mime_type":"application/json","accepts_all":[{"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","extra":{"name":"USD Coin","version":"2"},"payTo":"0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3","scheme":"exact","network":"base","mimeType":"application/json","resource":"https://lowpaymentfee.com/api/v1/cards/51","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-18T18:43:35.196Z"}],"sources":[{"listingId":"56631f70-e291-4a05-893d-ca174b6147a7","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/cards/51","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-18T18:43:35.196Z","lastSeenAt":"2026-04-22T10:31:28.744Z"}],"details":{"listingId":"56631f70-e291-4a05-893d-ca174b6147a7","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/cards/51 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <x402-payment-proof>\"","exampleRequest":null,"exampleResponse":null,"schema":{"input":{"type":"http","method":"GET","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"The platform lists APIs across data/analytics, AI/ML, finance/Web3, and infrastructure categories, all priced at $0.02/request.","source_url":"https://lowpaymentfee.com"},{"claim":"The x402 challenge shows maxAmountRequired of 20000 base units in USDC on Base network.","source_url":"https://lowpaymentfee.com/api/v1/cards/51"},{"claim":"USDC asset contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913.","source_url":"https://lowpaymentfee.com/api/v1/cards/51"},{"claim":"No API keys, no rate limits, instant access advertised.","source_url":"https://lowpaymentfee.com"}],"useCases":["Accessing a premium data or utility endpoint with per-request USDC micropayments","Integrating x402-compatible agents that pay for API calls on the Base network","Testing x402 payment flows against a live endpoint"],"bestFor":["Developers experimenting with x402 pay-per-request protocols","Agents that need keyless, pay-as-you-go API access on Base","Low-cost micropayment API consumption without subscriptions"],"notFor":["Users who need detailed API documentation or request/response schemas before integrating","High-volume use cases where per-request pricing may add up without volume discounts","Anyone without a Base-network USDC wallet"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:14:26.862Z"},"updatedAt":"2026-04-22T10:31:28.744Z"}}