{"id":"b16aa3ed-e361-4532-b7f3-a55843f77181","shortId":"VFah78","kind":"x402","title":"Pay-per-call API platform on Base (USDC) offering data, AI, finance, and utility endpoints at $0.02/request.","tagline":"Pay-per-call API platform on Base (USDC) offering data, AI, finance, and utility endpoints at $0.02/request.","description":"lowpaymentfee.com is an x402-enabled API platform that provides a broad catalog of pay-per-request endpoints settled in USDC on the Base network. The specific endpoint at `/api/v1/inbox/21` is listed as \"Premium API Access\" and costs up to $0.02 per call (20,000 base units of USDC with 6 decimals). No API keys or accounts are required; callers authenticate by attaching an x402 payment header with each request.\n\nThe wider platform advertises four endpoint categories: Data & Analytics (metrics, reports, data export, insights), AI & Machine Learning (sentiment analysis, text summarization, classification, embeddings), Finance & Web3 (price feeds, exchange rates, token quotes, gas estimates), and Infrastructure utilities (geocoding, validation, conversion, generation). All listed endpoints share the same $0.02/request pricing with no rate limits or minimum commitments.\n\nNote that the specific functionality behind `/api/v1/inbox/21` (\"Premium API Access\") is not documented beyond its title. There is no OpenAPI schema, no request/response examples, and the crawled docs pages (pricing, README, API) all returned only a \"Connect wallet\" prompt with no additional content. The endpoint is confirmed live via a valid 402 challenge, but what it actually returns upon successful payment is unknown.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","no-api-key","data-analytics","ai-inference","finance-data","utility-services"],"categories":["api-platform","llm","finance","geo"],"synonyms":["x402 API","pay-per-call API","USDC micropayment API","Base network API","lowpaymentfee","low payment fee API","crypto API gateway"],"warnings":["The specific functionality of /api/v1/inbox/21 ('Premium API Access') is completely undocumented — it is unclear what data or service it provides.","No OpenAPI schema, request format, or response examples are available for any endpoint on this platform.","All documentation pages (/api, /pricing, /README) returned only a 'Connect wallet' prompt with no usable content.","The broad catalog of endpoints (AI, finance, data, utils) is advertised on the landing page but none have been individually verified beyond this single inbox endpoint."],"endpointUrl":"https://lowpaymentfee.com/api/v1/inbox/21","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/inbox/21","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.300","qualityRationale":"The endpoint is confirmed live via a valid x402 402 challenge, but there is zero documentation on what /api/v1/inbox/21 actually does, no OpenAPI schema, no request/response examples, and the docs/pricing/README pages are empty beyond a wallet-connect prompt. The listing is essentially a stub with only pricing and liveness 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'/request':19,38,157 '0.02':18,37,80,156 '000':84 '20':83 '402':217 '6':90 'Base network API' 'USDC micropayment API' 'access':75,175 'account':96 'actual':222 'addit':207 'advertis':113 'ai':12,31,124 'ai-inference' 'analysi':128 'analyt':118 'api':5,24,45,74,93,174,197 'attach':102 'authent':100 'base':8,27,63,85 'behind':171 'beyond':179 'broad':50 'call':4,23,82 'caller':99 'catalog':51 'categori':116 'challeng':218 'classif':131 'commit':165 'confirm':212 'connect':202 'content':208 'convers':148 'cost':77 'crawl':192 'crypto API gateway' 'data':11,30,117,121 'data-analytics' 'decim':91 'doc':193 'document':178 'embed':132 'enabl':44 'endpoint':16,35,57,67,115,152,210 'estim':142 'exampl':189 'exchang':137 'export':122 'feed':136 'financ':13,32,133 'finance-data' 'four':114 'function':170 'gas':141 'generat':149 'geocod':146 'header':106 'infrastructur':144 'insight':123 'key':94 'learn':126 'limit':162 'list':71,151 'live':213 'low payment fee API' 'lowpaymentfee' 'lowpaymentfee.com':39 'machin':125 'metric':119 'minimum':164 'network':64 'no-api-key' 'note':166 'offer':10,29 'openapi':185 'page':194 'pay':2,21,54 'pay-per-cal':1,20 'pay-per-call API' 'pay-per-request':53 'payment':105,226 'per':3,22,55,81 'platform':6,25,46,112 'premium':73,173 'price':135,158,195 'prompt':204 'provid':48 'quot':140 'rate':138,161 'readm':196 'report':120 'request':56,109 'request/response':188 'requir':98 'return':199,223 'schema':186 'sentiment':127 'settl':58 'share':153 'specif':66,169 'success':225 'summar':130 'text':129 'titl':181 'token':139 'unit':86 'unknown':228 'upon':224 'usdc':9,28,60,88 'usdc-base' 'util':15,34,145 'utility-services' 'valid':147,216 'via':214 'wallet':203 'web3':134 'wider':111 'x402':43,104 'x402 API' 'x402-enabled':42 'x402-payment'","prices":[{"id":"d46c0086-9c40-4abd-92d6-49c23b72f3f5","listingId":"b16aa3ed-e361-4532-b7f3-a55843f77181","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/inbox/21","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:20.667Z"}],"sources":[{"listingId":"b16aa3ed-e361-4532-b7f3-a55843f77181","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/inbox/21","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:20.667Z","lastSeenAt":"2026-04-22T10:02:55.947Z"}],"details":{"listingId":"b16aa3ed-e361-4532-b7f3-a55843f77181","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/inbox/21 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <x402-payment-token>\" \\\n  -d '{}'","exampleRequest":null,"exampleResponse":null,"schema":{"input":{"type":"http","method":"GET","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"The endpoint returns a 402 challenge with maxAmountRequired of 20000 base units of USDC on Base network","source_url":"https://lowpaymentfee.com/api/v1/inbox/21"},{"claim":"USDC asset address 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base","source_url":"https://lowpaymentfee.com/api/v1/inbox/21"},{"claim":"Platform advertises $0.02/request pricing with no API keys, no rate limits, and instant access","source_url":"https://lowpaymentfee.com"},{"claim":"Four endpoint categories: Data & Analytics, AI & Machine Learning, Finance & Web3, Infrastructure","source_url":"https://lowpaymentfee.com"}],"useCases":["Accessing AI inference endpoints (sentiment, summarization, classification, embeddings) without API key management","Fetching real-time financial data such as token quotes, gas estimates, and exchange rates on a per-call basis","Running data analytics queries and exporting reports with micropayment-based access control","Using utility services like geocoding, validation, and data conversion via x402 payments"],"bestFor":["Agents or bots that need keyless, pay-as-you-go API access","Developers experimenting with x402 protocol micropayments on Base","Applications requiring low-cost, no-commitment access to diverse API categories"],"notFor":["Users who need detailed API documentation or guaranteed SLAs before integrating","High-volume production workloads where per-request crypto settlement overhead is impractical","Users without a Base-network USDC wallet"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:13:08.618Z"},"updatedAt":"2026-04-22T10:02:55.947Z"}}