{"id":"6e6314ec-2495-4ab6-82e3-73c061774c1a","shortId":"KdJns8","kind":"x402","title":"Pay-per-request API platform on Base (USDC) via x402 — $0.02/call, no API keys required.","tagline":"Pay-per-request API platform on Base (USDC) via x402 — $0.02/call, no API keys required.","description":"lowpaymentfee.com is a pay-per-request API platform that uses the x402 protocol to accept USDC payments on the Base network. The specific endpoint `/api/v1/inbox/149` is listed as \"Premium API Access\" and accepts POST requests, charging up to $0.02 per call (20,000 base units of USDC with 6 decimals). No API keys, accounts, or rate limits are advertised — callers simply attach an x402 payment header to each request.\n\nThe broader platform advertises multiple API 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 endpoints are listed at the same $0.02/request price point. However, the specific endpoint probed here (`/api/v1/inbox/149`) does not clearly map to any of the named categories on the landing page, and its actual functionality is undocumented.\n\nThe endpoint is live and returns a valid x402 challenge with scheme \"exact\" on the Base network, paying to address `0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3` in USDC (`0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`). The timeout is 300 seconds. No OpenAPI spec, detailed documentation, or example responses were found during the crawl — the /api, /pricing, and /README pages all returned only a \"Connect wallet\" prompt with no substantive content.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","no-api-key","post-endpoint","json-response"],"categories":["general","api-marketplace"],"synonyms":["low payment fee","x402 api","pay per call api","usdc api","base network api","micropayment api","402 payment api"],"warnings":["The specific endpoint /api/v1/inbox/149 has no documentation explaining what it does or what request/response formats it expects.","No OpenAPI spec or schema is available for any endpoint on the platform.","The /api, /pricing, and /README pages returned no useful content (only 'Connect wallet' prompts).","The 'inbox' path segment does not correspond to any of the advertised API categories, raising questions about what this endpoint actually provides."],"endpointUrl":"https://lowpaymentfee.com/api/v1/inbox/149","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/149","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, but the actual functionality of /api/v1/inbox/149 is completely undocumented. No OpenAPI spec, no example responses, and no description beyond the generic 'Premium API Access' label. The crawled docs pages were empty. The platform lists many API categories but this specific inbox endpoint doesn't map to any of 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'/api/v1/inbox/149':60,162 '/call':13,30 '/pricing':227 '/readme':229 '/request':153 '0.02':12,29,74,152 '000':78 '0x1a2b13e97f5f837c8f9fa1f95a1484b7c70d85f3':203 '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913':206 '20':77 '300':210 '402 payment api' '6':84 'accept':50,68 'access':66 'account':89 'actual':179 'address':202 'advertis':94,108 'ai':119 'analysi':123 'analyt':113 'api':5,15,22,32,42,65,87,110 'attach':97 'base':8,25,55,79,198 'base network api' 'broader':106 'call':76 'caller':95 'categori':111,172 'challeng':192 'charg':71 'classif':126 'clear':165 'connect':235 'content':241 'convers':143 'crawl':224 'data':112,116 'decim':85 'detail':215 'document':216 'embed':127 'endpoint':59,146,159,184 'estim':137 'exact':195 'exampl':218 'exchang':132 'export':117 'feed':131 'financ':128 'found':221 'function':180 'gas':136 'generat':144 'geocod':141 'header':101 'howev':156 'infrastructur':139 'insight':118 'json-response' 'key':16,33,88 'land':175 'learn':121 'limit':92 'list':62,148 'live':186 'low payment fee' 'lowpaymentfee.com':35 'machin':120 'map':166 'metric':114 'micropayment api' 'multipl':109 'name':171 'network':56,199 'no-api-key' 'openapi':213 'page':176,230 'pay':2,19,39,200 'pay per call api' 'pay-per-request':1,18,38 'payment':52,100 'per':3,20,40,75 'platform':6,23,43,107 'point':155 'post':69 'post-endpoint' 'premium':64 'price':130,154 'probe':160 'prompt':237 'protocol':48 'quot':135 'rate':91,133 'report':115 'request':4,21,41,70,104 'requir':17,34 'respons':219 'return':188,232 'scheme':194 'second':211 'sentiment':122 'simpli':96 'spec':214 'specif':58,158 'substant':240 'summar':125 'text':124 'timeout':208 'token':134 'undocu':182 'unit':80 'usdc':9,26,51,82,205 'usdc api' 'usdc-base' 'use':45 'util':140 'valid':142,190 'via':10,27 'wallet':236 'web3':129 'x402':11,28,47,99,191 'x402 api' 'x402-payment'","prices":[{"id":"1d042076-20f0-405b-bda8-7e3d67d78f5b","listingId":"6e6314ec-2495-4ab6-82e3-73c061774c1a","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/149","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:20.559Z"}],"sources":[{"listingId":"6e6314ec-2495-4ab6-82e3-73c061774c1a","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/inbox/149","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:20.559Z","lastSeenAt":"2026-04-22T04:02:33.179Z"}],"details":{"listingId":"6e6314ec-2495-4ab6-82e3-73c061774c1a","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/inbox/149 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <x402-payment-token>\" \\\n  -d '{}'","exampleRequest":{"url":"https://lowpaymentfee.com/api/v1/inbox/149","body":{},"method":"POST","headers":{"X-PAYMENT":"<x402-payment-token>","Content-Type":"application/json"}},"exampleResponse":null,"schema":{"input":{"type":"http","method":"GET","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"The endpoint returns a valid x402 challenge with maxAmountRequired of 20000 base units of USDC on Base network","source_url":"https://lowpaymentfee.com/api/v1/inbox/149"},{"claim":"The platform advertises $0.02/request pricing with no API keys, no rate limits, and instant access","source_url":"https://lowpaymentfee.com"},{"claim":"USDC asset address is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base","source_url":"https://lowpaymentfee.com/api/v1/inbox/149"},{"claim":"The platform lists Data & Analytics, AI & ML, Finance & Web3, and Infrastructure API categories","source_url":"https://lowpaymentfee.com"}],"useCases":["Programmatic access to a generic premium API endpoint via x402 micropayments","Agent-driven workflows that need keyless, pay-as-you-go API access on Base","Testing x402 protocol integrations with a low-cost live endpoint"],"bestFor":["Developers experimenting with x402 payment protocol","AI agents that need frictionless pay-per-call API access without credentials","Low-volume consumers who want no subscription or commitment"],"notFor":["Users who need well-documented, predictable API responses (functionality of this specific endpoint is unclear)","High-volume production workloads where per-request pricing at $0.02 may add up","Anyone requiring SLA guarantees or support"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:13:08.871Z"},"updatedAt":"2026-04-22T04:02:33.179Z"}}