Pay-per-call API platform on Base (USDC) covering data, AI, finance, and utility endpoints at $0.02/request.
What it does
lowpaymentfee.com is an x402-enabled API platform that offers a broad catalog of pay-per-request endpoints settled in USDC on the Base network. The specific endpoint at `/api/v1/invoices/21` is listed as "Premium API Access" and returns an x402 challenge requesting up to 20,000 base units of USDC (i.e., $0.02) per call. The platform advertises no API keys, no rate limits, and instant access — callers simply attach an x402 payment header to each request.
The site's landing page lists four endpoint 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 listed endpoints share the same $0.02/request price point.
However, documentation is essentially absent — the /docs, /pricing, /api, and /README pages all render only a "Connect wallet" prompt with no further content. There is no OpenAPI schema, no request/response examples, and no description of what the `/api/v1/invoices/21` endpoint specifically returns. The endpoint is live (402 challenge confirmed), but without documentation it is unclear what payload to send or what response to expect.
Capabilities
Use cases
- —Accessing AI inference endpoints (sentiment, summarization, classification, embeddings) without API key management
- —Fetching real-time financial data such as token quotes, gas estimates, and exchange rates
- —Running utility operations like geocoding, validation, and data conversion on a per-call payment basis
Fit
Best for
- —Developers who want zero-signup, pay-as-you-go API access
- —Agents that can settle USDC payments on Base via x402
- —Projects needing low-cost micropayment-gated endpoints
Not for
- —Users who need detailed API documentation or OpenAPI specs before integrating
- —Applications requiring high-throughput bulk access with negotiated pricing
- —Teams that cannot transact in USDC on the Base network
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/invoices/21 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-token>"Endpoint
Quality
The endpoint is live and returns a valid x402 challenge, but documentation is effectively nonexistent — all doc pages show only 'Connect wallet'. There is no OpenAPI schema, no request/response examples, and no explanation of what the invoices/21 endpoint actually does. The listing is largely a stub.
Warnings
- —No documentation available — /docs, /pricing, /api, and /README pages all render only 'Connect wallet'
- —No OpenAPI or schema definition found for any endpoint
- —The specific purpose of /api/v1/invoices/21 ('Premium API Access') is undocumented — unclear what it returns
- —The broad catalog of endpoints listed on the homepage cannot be verified for functionality
Citations
- —The endpoint returns an x402 challenge requesting up to 20,000 base units of USDC ($0.02) on Base networkhttps://lowpaymentfee.com/api/v1/invoices/21
- —The platform lists endpoints across Data & Analytics, AI & ML, Finance & Web3, and Infrastructure categories all at $0.02/requesthttps://lowpaymentfee.com
- —The site advertises no API keys, no rate limits, and instant accesshttps://lowpaymentfee.com
- —Documentation pages (/docs, /pricing, /api, /README) render only 'Connect wallet'https://lowpaymentfee.com/docs