{"id":"61da8bf2-999c-4619-8450-5c3fed729a3c","shortId":"x9sQvb","kind":"x402","title":"Pay-per-call API platform on Base (USDC) — $0.02/request, no API keys required.","tagline":"Pay-per-call API platform on Base (USDC) — $0.02/request, no API keys required.","description":"lowpaymentfee.com is an x402-enabled API platform that offers a broad catalog of endpoints spanning data analytics, AI/ML inference, finance/Web3 data, and infrastructure utilities. Every endpoint is priced at $0.02 per request, payable in USDC on the Base network via the x402 protocol. There are no API keys, no rate limits, and no subscription commitments — callers simply attach an x402 payment header to each request.\n\nThe specific endpoint at `/api/v1/inbox/53` is listed as \"Premium API Access\" but its exact functionality is not documented beyond that label. The broader platform advertises endpoints for sentiment analysis, text summarization, classification, embeddings, price feeds, exchange rates, token quotes, gas estimates, geocoding, validation, conversion, and data generation. The x402 challenge for this endpoint confirms it accepts POST requests, settles in USDC (contract 0x8335…) on Base, and requires a maximum of 20,000 base units (i.e., $0.02 given USDC's 6 decimals).\n\nBecause the `/api/v1/inbox/53` endpoint lacks specific documentation about its input/output schema and purpose, callers should treat it as an opaque premium endpoint. The platform's landing page is live and the 402 challenge is well-formed, but no OpenAPI spec, detailed docs, or example responses are available.","tags":[],"capabilities":["x402-payment","usdc-base","pay-per-request","no-api-key","post-endpoint","json-response"],"categories":["api-platform","infrastructure"],"synonyms":["x402 API","micropayment API","pay-per-call","USDC API","Base network API","lowpaymentfee","low payment fee"],"warnings":["The endpoint '/api/v1/inbox/53' has no documentation describing what it does or what inputs it expects.","No OpenAPI specification or output schema is available for any endpoint on this platform.","The /api, /pricing, and /README pages all returned only a 'Connect wallet' prompt with no useful content.","The 'inbox' path segment suggests this may be a mailbox or message-drop endpoint, but this is purely speculative."],"endpointUrl":"https://lowpaymentfee.com/api/v1/inbox/53","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/53","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.350","qualityRationale":"The endpoint is live and returns a well-formed x402 402 challenge, but the specific endpoint '/api/v1/inbox/53' has no documentation about its purpose, input schema, or output schema. No OpenAPI spec, no examples, and the 'Premium API Access' label is entirely generic. The broader platform catalog is visible but this particular inbox endpoint is 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'/request':11,26 '0.02':10,25,61,172 '000':168 '0x8335':159 '20':167 '402':209 '6':176 'Base network API' 'USDC API' 'accept':152 'access':107 'advertis':121 'ai/ml':49 'analysi':125 'analyt':48 'api':5,13,20,28,37,78,106 'attach':89 'avail':225 'base':8,23,69,161,169 'beyond':115 'broad':42 'broader':119 'call':4,19 'caller':87,191 'catalog':43 'challeng':146,210 'classif':128 'commit':86 'confirm':150 'contract':158 'convers':140 'data':47,52,142 'decim':177 'detail':219 'doc':220 'document':114,184 'embed':129 'enabl':36 'endpoint':45,57,99,122,149,181,199 'estim':137 'everi':56 'exact':110 'exampl':222 'exchang':132 'feed':131 'finance/web3':51 'form':214 'function':111 'gas':136 'generat':143 'geocod':138 'given':173 'header':93 'i.e':171 'infer':50 'infrastructur':54 'input/output':187 'json-response' 'key':14,29,79 'label':117 'lack':182 'land':203 'limit':82 'list':103 'live':206 'low payment fee' 'lowpaymentfee' 'lowpaymentfee.com':31 'maximum':165 'micropayment API' 'network':70 'no-api-key' 'offer':40 'opaqu':197 'openapi':217 'page':204 'pay':2,17 'pay-per-cal':1,16 'pay-per-call' 'pay-per-request' 'payabl':64 'payment':92 'per':3,18,62 'platform':6,21,38,120,201 'post':153 'post-endpoint' 'premium':105,198 'price':59,130 'protocol':74 'purpos':190 'quot':135 'rate':81,133 'request':63,96,154 'requir':15,30,163 'respons':223 'schema':188 'sentiment':124 'settl':155 'simpli':88 'span':46 'spec':218 'specif':98,183 'subscript':85 'summar':127 'text':126 'token':134 'treat':193 'unit':170 'usdc':9,24,66,157,174 'usdc-base' 'util':55 'valid':139 'via':71 'well':213 'well-form':212 'x402':35,73,91,145 'x402 API' 'x402-enabled':34 'x402-payment'","prices":[{"id":"edeee707-1945-4a7e-bfaf-05d81a821a74","listingId":"61da8bf2-999c-4619-8450-5c3fed729a3c","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/53","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-21T18:32:21.918Z"}],"sources":[{"listingId":"61da8bf2-999c-4619-8450-5c3fed729a3c","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/inbox/53","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-21T18:32:21.918Z","lastSeenAt":"2026-04-22T11:32:57.721Z"}],"details":{"listingId":"61da8bf2-999c-4619-8450-5c3fed729a3c","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/inbox/53 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <x402-payment-token>\" \\\n  -d '{}'","exampleRequest":{"url":"https://lowpaymentfee.com/api/v1/inbox/53","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":"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":"x402 challenge confirms USDC on Base with maxAmountRequired of 20000 base units ($0.02).","source_url":"https://lowpaymentfee.com/api/v1/inbox/53"},{"claim":"USDC asset contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913.","source_url":"https://lowpaymentfee.com/api/v1/inbox/53"},{"claim":"Platform lists endpoints for analytics, AI/ML, finance/Web3, and infrastructure utilities.","source_url":"https://lowpaymentfee.com"}],"useCases":["Programmatic access to a premium API endpoint without needing API keys or subscriptions","Agent-driven workflows that pay per call using USDC on Base","Testing x402 payment flows against a live, low-cost endpoint"],"bestFor":["Developers experimenting with x402 payment protocol","AI agents that need keyless, pay-as-you-go API access","Low-cost per-request usage without rate limits"],"notFor":["Users who need detailed documentation or guaranteed SLAs before integrating","Anyone without a Base-network USDC wallet or x402-compatible client"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:13:08.242Z"},"updatedAt":"2026-04-22T11:32:57.721Z"}}