{"id":"e97b619d-a617-454e-bd08-f928b8c8cf40","shortId":"ySQddX","kind":"x402","title":"Pay-per-call API platform on Base with $0.02 USDC requests via x402 — no keys, no rate limits.","tagline":"Pay-per-call API platform on Base with $0.02 USDC requests via x402 — no keys, no rate limits.","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/50` is listed as \"Premium API Access\" and charges up to 20,000 base units of USDC (i.e., $0.02 per request, since USDC uses 6 decimals). Payment is handled inline via the X-PAYMENT header — no API keys, accounts, or subscriptions are required.\n\nThe broader platform advertises multiple API categories including 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.\n\nHowever, the specific functionality of the `/api/v1/inbox/50` endpoint is unclear. The path suggests a mailbox or inbox resource (item #50), but no documentation, request schema, or response schema is available beyond the generic \"Premium API Access\" label. The endpoint accepts POST requests and returns `application/json`. Without further documentation, the exact input parameters and response format remain unknown.","tags":[],"capabilities":["x402-payment","usdc-base-network","pay-per-request","no-api-key","post-endpoint","json-response"],"categories":["api-platform","infrastructure"],"synonyms":["low payment fee","micropayment API","x402 API","USDC pay-per-call","Base network API","paywall API","inbox API"],"warnings":["No documentation available for the /api/v1/inbox/50 endpoint — its purpose and expected input/output are unknown","No OpenAPI spec, no request schema, and no response schema provided","Crawled /api, /pricing, and /README pages returned no useful content (only 'Connect wallet')","The 'inbox/50' path semantics are unclear — could be a messaging inbox, a numbered resource, or something else entirely"],"endpointUrl":"https://lowpaymentfee.com/api/v1/inbox/50","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/50","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.300","qualityRationale":"The x402 challenge is live and pricing is clear ($0.02 USDC on Base), but there is no documentation, no request/response schema, and no explanation of what the /api/v1/inbox/50 endpoint actually does. The crawled pages beyond the homepage returned only 'Connect wallet' with no useful content. This is effectively a stub 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'/request':157 '0.02':10,29,82,156 '000':76 '20':75 '50':179 '6':88 'Base network API' 'USDC pay-per-call' 'accept':54,199 'access':70,195 'account':103 'advertis':111 'ai':123 'analysi':127 'analyt':117 'api':5,24,46,69,101,113,194 'application/json':204 'avail':189 'base':8,27,59,77 'beyond':190 'broader':109 'call':4,23 'categori':114 'charg':72 'classif':130 'convers':147 'data':116,120 'decim':89 'document':182,207 'embed':131 'endpoint':63,150,167,198 'estim':141 'exact':209 'exchang':136 'export':121 'feed':135 'financ':132 'format':214 'function':163 'gas':140 'generat':148 'generic':192 'geocod':145 'handl':92 'header':99 'howev':160 'i.e':81 'inbox':176 'inbox API' 'includ':115 'infrastructur':143 'inlin':93 'input':210 'insight':122 'item':178 'json-response' 'key':16,35,102 'label':196 'learn':125 'limit':19,38 'list':66,152 'low payment fee' 'lowpaymentfee.com':39 'machin':124 'mailbox':174 'metric':118 'micropayment API' 'multipl':112 'network':60 'no-api-key' 'paramet':211 'path':171 'pay':2,21,43 'pay-per-cal':1,20 'pay-per-request':42 'payment':56,90,98 'paywall API' 'per':3,22,44,83 'platform':6,25,47,110 'point':159 'post':200 'post-endpoint' 'premium':68,193 'price':134,158 'protocol':52 'quot':139 'rate':18,37,137 'remain':215 'report':119 'request':12,31,45,84,183,201 'requir':107 'resourc':177 'respons':186,213 'return':203 'schema':184,187 'sentiment':126 'sinc':85 'specif':62,162 'subscript':105 'suggest':172 'summar':129 'text':128 'token':138 'unclear':169 'unit':78 'unknown':216 'usdc':11,30,55,80,86 'usdc-base-network' 'use':49,87 'util':144 'valid':146 'via':13,32,94 'web3':133 'without':205 'x':97 'x-payment':96 'x402':14,33,51 'x402 API' 'x402-payment'","prices":[{"id":"c0538f4a-f39b-4b90-a1fd-ef0fb61fa53c","listingId":"e97b619d-a617-454e-bd08-f928b8c8cf40","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/50","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:31.683Z"}],"sources":[{"listingId":"e97b619d-a617-454e-bd08-f928b8c8cf40","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/inbox/50","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:31.683Z","lastSeenAt":"2026-04-22T04:02:46.106Z"}],"details":{"listingId":"e97b619d-a617-454e-bd08-f928b8c8cf40","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/inbox/50 \\\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 charges up to 20,000 base units of USDC (asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913) on Base network, which equals $0.02","source_url":"https://lowpaymentfee.com/api/v1/inbox/50"},{"claim":"The platform advertises $0.02/request pricing with no API keys, no rate limits, and instant access on the Base network","source_url":"https://lowpaymentfee.com"},{"claim":"Available API categories include Data & Analytics, AI & Machine Learning, Finance & Web3, and Infrastructure utilities","source_url":"https://lowpaymentfee.com"},{"claim":"Payment is to address 0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3 with a max timeout of 300 seconds","source_url":"https://lowpaymentfee.com/api/v1/inbox/50"}],"useCases":["Accessing a premium inbox or messaging resource with per-call USDC micropayments","Integrating pay-per-use API calls into agent workflows without managing API keys","Programmatic access to platform services settled on Base L2"],"bestFor":["Developers wanting zero-friction API access without signup or key management","Agents that can settle x402 payments in USDC on Base","Use cases requiring low-cost per-request billing ($0.02/call)"],"notFor":["Users who need detailed API documentation or guaranteed SLAs before integrating","High-volume consumers who would benefit from bulk pricing or subscriptions","Anyone unable to transact in USDC on the Base network"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:12:52.041Z"},"updatedAt":"2026-04-22T04:02:46.106Z"}}