{"id":"5d0309db-28a1-40fb-a7dc-fd2a433e11d0","shortId":"XyUDdL","kind":"x402","title":"Pay-per-call premium API access on Base via x402 — $0.02/request in USDC.","tagline":"Pay-per-call premium API access on Base via x402 — $0.02/request in USDC.","description":"This endpoint at lowpaymentfee.com is part of a broader platform offering pay-per-request APIs across multiple categories including data & analytics, AI & machine learning, finance & Web3, and infrastructure utilities. The specific endpoint `/api/v1/inbox/156` is labeled \"Premium API Access\" but its exact functionality is not documented beyond that label. The platform advertises a uniform $0.02 per request pricing model with no API keys, no rate limits, and instant access.\n\nPayment is handled via the x402 protocol on the Base network using USDC (contract 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913). The probe confirms the endpoint is live, returning a 402 challenge with a maxAmountRequired of 20000 base units, which equals $0.02 (USDC uses 6 decimals). The payment scheme is \"exact\" with a 300-second timeout. No OpenAPI schema, detailed documentation, or example request/response bodies were found for this specific endpoint. The broader site lists sibling endpoints for sentiment analysis, text summarization, geocoding, price feeds, and more — all at the same $0.02 price point.\n\nBecause the endpoint path (`/inbox/156`) does not clearly map to any of the documented API categories and no input/output schema is provided, the actual functionality of this particular endpoint remains unclear. Callers should treat this as an opaque premium endpoint until further documentation is available.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","no-api-key","http-post"],"categories":["api-marketplace","infrastructure"],"synonyms":["lowpaymentfee","low payment fee API","x402 API","pay-per-call API","USDC micropayment API","Base network API","premium API access"],"warnings":["No OpenAPI or input/output schema available for this endpoint","The endpoint path /api/v1/inbox/156 does not match any of the documented API categories on the site","No documentation pages rendered meaningful content (pricing, README, and /api pages only showed 'Connect wallet')","Actual functionality behind 'Premium API Access' is unknown — treat as opaque"],"endpointUrl":"https://lowpaymentfee.com/api/v1/inbox/156","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/156","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, no OpenAPI schema, no example requests or responses, and the endpoint path '/inbox/156' does not correspond to any documented API category. Functionality is essentially 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'/inbox/156':192 '/request':13,28 '0.02':12,27,85,135,185 '0x833589fcd6edb6e08f4c7c32d4f71b54bda02913':114 '20000':130 '300':147 '402':124 '6':138 'Base network API' 'USDC micropayment API' 'access':7,22,69,99 'across':47 'actual':211 'advertis':82 'ai':53 'analysi':173 'analyt':52 'api':6,21,46,68,92,202 'avail':232 'base':9,24,109,131 'beyond':77 'bodi':158 'broader':39,166 'call':4,19 'caller':219 'categori':49,203 'challeng':125 'clear':195 'confirm':117 'contract':113 'data':51 'decim':139 'detail':153 'document':76,154,201,230 'endpoint':32,63,119,164,170,190,216,227 'equal':134 'exact':72,144 'exampl':156 'feed':178 'financ':56 'found':160 'function':73,212 'geocod':176 'handl':102 'http-post' 'includ':50 'infrastructur':59 'input/output':206 'instant':98 'key':93 'label':66,79 'learn':55 'limit':96 'list':168 'live':121 'low payment fee API' 'lowpaymentfee' 'lowpaymentfee.com':34 'machin':54 'map':196 'maxamountrequir':128 'model':89 'multipl':48 'network':110 'no-api-key' 'offer':41 'opaqu':225 'openapi':151 'part':36 'particular':215 'path':191 'pay':2,17,43 'pay-per-cal':1,16 'pay-per-call API' 'pay-per-request':42 'payment':100,141 'per':3,18,44,86 'platform':40,81 'point':187 'premium':5,20,67,226 'premium API access' 'price':88,177,186 'probe':116 'protocol':106 'provid':209 'rate':95 'remain':217 'request':45,87 'request/response':157 'return':122 'schema':152,207 'scheme':142 'second':148 'sentiment':172 'sibl':169 'site':167 'specif':62,163 'summar':175 'text':174 'timeout':149 'treat':221 'unclear':218 'uniform':84 'unit':132 'usdc':15,30,112,136 'usdc-base' 'use':111,137 'util':60 'via':10,25,103 'web3':57 'x402':11,26,105 'x402 API' 'x402-payment'","prices":[{"id":"f0b4c8e4-8a40-4958-bf17-bdeed89f8008","listingId":"5d0309db-28a1-40fb-a7dc-fd2a433e11d0","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/156","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:20.495Z"}],"sources":[{"listingId":"5d0309db-28a1-40fb-a7dc-fd2a433e11d0","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/inbox/156","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:20.495Z","lastSeenAt":"2026-04-22T07:32:22.936Z"}],"details":{"listingId":"5d0309db-28a1-40fb-a7dc-fd2a433e11d0","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/inbox/156 \\\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 platform advertises $0.02 per request with no API keys, no rate limits, and instant access on Base network","source_url":"https://lowpaymentfee.com"},{"claim":"The x402 challenge returns maxAmountRequired of 20000 base units in USDC on Base with a 300-second timeout","source_url":"https://lowpaymentfee.com/api/v1/inbox/156"},{"claim":"USDC contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","source_url":"https://lowpaymentfee.com/api/v1/inbox/156"},{"claim":"Sibling endpoints include analytics, AI (sentiment, summarize, classify, embeddings), finance, and utility APIs","source_url":"https://lowpaymentfee.com"}],"useCases":["Programmatic access to premium API services without subscription or API key management","Agent-driven workflows that need on-demand paid endpoints settled in USDC on Base","Testing x402 payment flows against a live, low-cost endpoint"],"bestFor":["Developers exploring x402 payment protocol integrations","AI agents needing frictionless pay-per-call API access","Users who want to avoid API key registration and rate limits"],"notFor":["Users who need detailed documentation or guaranteed SLAs before calling","Anyone requiring free or high-volume batch access at lower marginal cost","Use cases that need a well-defined input/output contract (no schema available)"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:13:08.992Z"},"updatedAt":"2026-04-22T07:32:22.936Z"}}