{"id":"3027e320-abdc-4e08-9ba4-c36f14a0d674","shortId":"kU9WDD","kind":"x402","title":"US 2021 tax return data via x402 micropayment on Base for $0.02 per request.","tagline":"US 2021 tax return data via x402 micropayment on Base for $0.02 per request.","description":"This endpoint at lowpaymentfee.com provides access to US tax return data for the 2021 tax year. It is part of a broader platform offering dozens of pay-per-call API endpoints spanning data analytics, AI/ML inference, finance, crypto, and utility services — all gated behind the x402 payment protocol on the Base network.\n\nThe specific endpoint `/api/v1/tax/returns/2021` accepts POST requests and returns JSON. Payment is settled in USDC (USD Coin) on Base. The x402 challenge advertises a maxAmountRequired of 20,000 base units, which at 6 decimals for USDC equals $0.02 per request — consistent with the platform's uniform $0.02/request pricing. No API keys are required; access is granted per-call via the X-PAYMENT header. The platform advertises no rate limits and instant access.\n\nDocumentation is extremely sparse. The docs, API, pricing, and README pages all render only a \"Connect wallet\" prompt with no substantive content. There is no OpenAPI schema, no request/response examples, and no description of what fields the tax return data contains or what input parameters the POST body expects. The endpoint is confirmed live (returns a proper 402 challenge), but the actual data content and request format must be discovered by the caller.","tags":[],"capabilities":["x402-payment","usdc-settlement","base-network","tax-data","json-api","pay-per-call","no-api-key"],"categories":["finance","data"],"synonyms":["tax return API","2021 tax data","IRS tax return","US tax filing data","tax records API","x402 tax endpoint"],"warnings":["No documentation available — docs, API, pricing, and README pages all show only 'Connect wallet' with no content","No OpenAPI or request/response schema provided; request body format is unknown","The nature and source of the 'tax return' data is unclear — it is inferred only from the URL path","This endpoint appears to deal with tax/financial data which may be subject to regulatory requirements"],"endpointUrl":"https://lowpaymentfee.com/api/v1/tax/returns/2021","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/tax/returns/2021","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}]},"qualityScore":"0.300","qualityRationale":"The endpoint is confirmed live with a valid x402 402 challenge and clear pricing ($0.02 USDC on Base). However, there is no documentation, no OpenAPI schema, no request/response examples, and no description of what data is actually returned. The tax return data claim is inferred solely from the URL path. This is effectively a stub 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'/request':129 '0.02':12,26,119,128 '000':109 '20':108 '2021':2,16,42 '2021 tax data' '402':214 '6':114 'IRS tax return' 'US tax filing data' 'accept':86 'access':34,136,156 'actual':218 'advertis':104,150 'ai/ml':64 'analyt':63 'api':59,132,163 'base':10,24,80,100,110 'base-network' 'behind':73 'bodi':204 'broader':50 'call':58,141 'caller':229 'challeng':103,215 'coin':98 'confirm':209 'connect':172 'consist':122 'contain':197 'content':178,220 'crypto':67 'data':5,19,39,62,196,219 'decim':115 'descript':189 'discov':226 'doc':162 'document':157 'dozen':53 'endpoint':30,60,84,207 'equal':118 'exampl':186 'expect':205 'extrem':159 'field':192 'financ':66 'format':223 'gate':72 'grant':138 'header':147 'infer':65 'input':200 'instant':155 'json':91 'json-api' 'key':133 'limit':153 'live':210 'lowpaymentfee.com':32 'maxamountrequir':106 'micropay':8,22 'must':224 'network':81 'no-api-key' 'offer':52 'openapi':182 'page':167 'paramet':201 'part':47 'pay':56 'pay-per-cal':55 'pay-per-call' 'payment':76,92,146 'per':13,27,57,120,140 'per-cal':139 'platform':51,125,149 'post':87,203 'price':130,164 'prompt':174 'proper':213 'protocol':77 'provid':33 'rate':152 'readm':166 'render':169 'request':14,28,88,121,222 'request/response':185 'requir':135 'return':4,18,38,90,195,211 'schema':183 'servic':70 'settl':94 'span':61 'spars':160 'specif':83 'substant':177 'tax':3,17,37,43,194 'tax records API' 'tax return API' 'tax-data' 'uniform':127 'unit':111 'us':1,15,36 'usd':97 'usdc':96,117 'usdc-settlement' 'util':69 'via':6,20,142 'wallet':173 'x':145 'x-payment':144 'x402':7,21,75,102 'x402 tax endpoint' 'x402-payment' 'year':44","prices":[{"id":"1473a915-ea33-4a22-a6cb-ea07838207f9","listingId":"3027e320-abdc-4e08-9ba4-c36f14a0d674","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/tax/returns/2021","description":"Premium API Access","outputSchema":{"input":{"type":"http","method":"GET","discoverable":true}},"maxAmountRequired":"20000","maxTimeoutSeconds":300}],"asset_contract":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","max_timeout_seconds":300},"createdAt":"2026-04-18T18:57:06.307Z"}],"sources":[{"listingId":"3027e320-abdc-4e08-9ba4-c36f14a0d674","source":"x402_bazaar","sourceId":"https://lowpaymentfee.com/api/v1/tax/returns/2021","sourceUrl":"https://api.cdp.coinbase.com/platform/v2/x402/discovery/resources","isPrimary":true,"firstSeenAt":"2026-04-18T18:57:06.307Z","lastSeenAt":"2026-04-26T15:33:15.583Z"}],"details":{"listingId":"3027e320-abdc-4e08-9ba4-c36f14a0d674","quickStartSnippet":"curl -X POST https://lowpaymentfee.com/api/v1/tax/returns/2021 \\\n  -H \"Content-Type: application/json\" \\\n  -H \"X-PAYMENT: <x402-payment-token>\"","exampleRequest":null,"exampleResponse":null,"schema":{"input":{"type":"http","method":"GET","discoverable":true}},"openapiUrl":null,"agentsTxtUrl":null,"citations":[{"claim":"The endpoint returns a 402 challenge with maxAmountRequired of 20000 base units in USDC on Base network","source_url":"https://lowpaymentfee.com/api/v1/tax/returns/2021"},{"claim":"Platform-wide pricing is $0.02 per request with no API keys, no rate limits, and instant access","source_url":"https://lowpaymentfee.com"},{"claim":"USDC asset contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","source_url":"https://lowpaymentfee.com/api/v1/tax/returns/2021"}],"useCases":["Retrieving US 2021 tax return data programmatically","Integrating tax data into financial analysis workflows","Agent-driven tax document lookups with micropayments"],"bestFor":["Developers needing on-demand tax return data without subscription commitments","AI agents that can pay per-call via x402 on Base","Applications requiring 2021 US tax year information"],"notFor":["Users who need comprehensive multi-year tax data (only 2021 is confirmed at this path)","Anyone requiring detailed API documentation or schema validation before integration","Non-crypto users who cannot settle payments in USDC on Base"],"kindDetails":{"x402_version":1,"resource_type":"http","bazaar_last_updated":"2026-02-17T23:13:47.75Z"},"updatedAt":"2026-04-26T15:33:15.583Z"}}