{"id":"81e9fc73-5243-422d-92ce-0c1867446991","shortId":"NEGbNJ","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 `/api/v1/inbox/143` is listed as \"Premium API Access\" and costs up to $0.02 per call (20,000 base units of USDC with 6 decimals). Payment is handled via the x402 protocol — no API keys, no subscriptions, no rate limits. Callers attach an `X-PAYMENT` header with a signed payment proof and receive the response immediately.\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.\n\nThe `/api/v1/inbox/143` endpoint itself has no public documentation beyond its title. There is no OpenAPI spec, no request/response schema, and no usage examples available from the crawled pages. The endpoint is confirmed live — it returns a valid x402 402 challenge with scheme \"exact\" on the Base network, paying to address `0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3` using USDC (`0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`). The method is POST and the response MIME type is `application/json`.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","json-api","post-method","no-api-key","no-rate-limit"],"categories":["api-platform","infrastructure"],"synonyms":["lowpaymentfee","low payment fee API","x402 API","USDC pay-per-call","Base network API","micropayment API","premium API access"],"warnings":["No OpenAPI or schema documentation available for this endpoint","The purpose of /api/v1/inbox/143 ('Premium API Access') is completely undocumented — it is unclear what data or service it provides","No request body schema or response schema is published","The /api, /pricing, and /README pages all returned only a 'Connect wallet' prompt with no useful content","Cannot verify what the endpoint actually returns upon successful payment"],"endpointUrl":"https://lowpaymentfee.com/api/v1/inbox/143","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/143","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.350","qualityRationale":"The endpoint is confirmed live with a valid x402 402 challenge, but there is no OpenAPI spec, no request/response schema, no documentation for what this specific endpoint does, and no examples. The 'Premium API Access' title is entirely generic. The broader site lists many endpoints but provides no detail on any of 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'/request':19,38,170 '0.02':18,37,79,169 '000':83 '0x1a2b13e97f5f837c8f9fa1f95a1484b7c70d85f3':222 '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913':225 '20':82 '402':210 '6':89 'Base network API' 'USDC pay-per-call' 'access':74 'address':221 'advertis':126 'ai':12,31,137 'analysi':141 'analyt':131 'api':5,24,45,73,99 'application/json':236 'attach':107 'avail':195 'base':8,27,63,84,217 'beyond':180 'broad':50 'call':4,23,81 'caller':106 'catalog':51 'categori':129 'challeng':211 'classif':144 'confirm':203 'convers':161 'cost':76 'crawl':198 'data':11,30,130,134 'decim':90 'document':179 'embed':145 'enabl':44 'endpoint':16,35,57,67,128,165,174,201 'estim':155 'exact':214 'exampl':194 'exchang':150 'export':135 'feed':149 'financ':13,32,146 'four':127 'gas':154 'generat':162 'geocod':159 'handl':93 'header':112 'immedi':122 'infrastructur':157 'insight':136 'json-api' 'key':100 'learn':139 'limit':105 'list':70,164 'live':204 'low payment fee API' 'lowpaymentfee' 'lowpaymentfee.com':39 'machin':138 'method':227 'metric':132 'micropayment API' 'mime':233 'network':64,218 'no-api-key' 'no-rate-limit' 'offer':10,29 'openapi':186 'page':199 'pay':2,21,54,219 'pay-per-cal':1,20 'pay-per-request':53 'payment':91,111,116 'per':3,22,55,80 'platform':6,25,46,125 'post':229 'post-method' 'premium':72 'premium API access' 'price':148,171 'proof':117 'protocol':97 'provid':48 'public':178 'quot':153 'rate':104,151 'receiv':119 'report':133 'request':56 'request/response':189 'respons':121,232 'return':206 'schema':190 'scheme':213 'sentiment':140 'settl':58 'share':166 'sign':115 'spec':187 'specif':66 'subscript':102 'summar':143 'text':142 'titl':182 'token':152 'type':234 'unit':85 'usag':193 'usdc':9,28,60,87,224 'usdc-base' 'use':223 'util':15,34,158 'valid':160,208 'via':94 'web3':147 'wider':124 'x':110 'x-payment':109 'x402':43,96,209 'x402 API' 'x402-enabled':42 'x402-payment'","prices":[{"id":"9fcb8a01-f177-413b-8cfc-d9df6e2f460a","listingId":"81e9fc73-5243-422d-92ce-0c1867446991","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/143","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:20.318Z"}],"sources":[{"listingId":"81e9fc73-5243-422d-92ce-0c1867446991","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/inbox/143","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:20.318Z","lastSeenAt":"2026-04-22T19:03:19.631Z"}],"details":{"listingId":"81e9fc73-5243-422d-92ce-0c1867446991","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/inbox/143 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <signed-x402-payment-proof>\" \\\n  -d '{}'","exampleRequest":null,"exampleResponse":null,"schema":{"input":{"type":"http","method":"GET","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"The endpoint returns a valid x402 402 challenge with maxAmountRequired of 20000 base units of USDC on Base","source_url":"https://lowpaymentfee.com/api/v1/inbox/143"},{"claim":"All listed endpoints cost $0.02 per request with no API keys, no rate limits, and instant access","source_url":"https://lowpaymentfee.com"},{"claim":"The platform offers endpoints in Data & Analytics, AI & ML, Finance & Web3, and Infrastructure categories","source_url":"https://lowpaymentfee.com"},{"claim":"USDC contract address is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base network","source_url":"https://lowpaymentfee.com/api/v1/inbox/143"}],"useCases":["Programmatic access to a premium API endpoint without needing API keys or subscriptions","Agent-driven workflows that need to pay per call using USDC on Base","Testing x402 payment flows against a live endpoint"],"bestFor":["Developers or agents wanting zero-signup, pay-per-use API access","x402 protocol integrators looking for live endpoints on Base","Scenarios requiring no rate limits and instant access"],"notFor":["Users who need detailed API documentation or guaranteed SLAs before integrating","Anyone without USDC on the Base network or an x402-compatible client"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:13:09.273Z"},"updatedAt":"2026-04-22T19:03:19.631Z"}}