Pay-per-request premium API access via x402 on Base, settled in USDC at $0.02/call.
What it does
lowpaymentfee.com is a multi-category API platform that gates every endpoint behind the x402 payment protocol, settling in USDC on the Base network. The specific endpoint at `/api/v1/invoices/43` is listed as "Premium API Access" and requires a maximum payment of 20,000 base units of USDC (0.02 USD) per request. The platform advertises no API keys, no rate limits, and instant access — callers simply attach an X-PAYMENT header with a valid x402 payment proof.
The broader site offers endpoints across four 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 endpoints are uniformly priced at $0.02 per request.
This particular endpoint (`/api/v1/invoices/43`) is confirmed live, returning a proper 402 challenge with x402 version 1. The payment is directed to address `0x1A2B13E97f5F837C8F9FA1F95a1484B7C70d85F3` using the USDC contract on Base (`0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`). The endpoint accepts POST requests and returns `application/json`. Documentation beyond the landing page is extremely thin — the docs, API, pricing, and README pages all render only a "Connect wallet" prompt with no substantive content.
Capabilities
Use cases
- —Programmatic access to premium data or services without API key registration
- —Agent-driven workflows that need instant, keyless API access with crypto micropayments
- —Testing x402 payment protocol integrations against a live endpoint
Fit
Best for
- —Developers or agents with USDC on Base who want frictionless pay-per-call access
- —Exploring x402 protocol mechanics with a low-cost live endpoint
- —Scenarios requiring no signup, no rate limits, and immediate access
Not for
- —Users who need detailed API documentation or OpenAPI schemas before integrating
- —High-volume use cases where $0.02/request adds up and subscription pricing would be cheaper
- —Users without a Base-compatible wallet or USDC holdings
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/invoices/43 \
-H "X-PAYMENT: <x402-payment-proof>" \
-H "Content-Type: application/json"Endpoint
Quality
The endpoint is confirmed live with a valid 402 challenge and clear pricing ($0.02 USDC on Base). However, there is no OpenAPI schema, no documentation beyond a landing page, no example request/response bodies, and the specific functionality of `/api/v1/invoices/43` is entirely opaque. The docs, pricing, and README pages are all empty stubs.
Warnings
- —No OpenAPI or schema documentation available — the actual request body and response format for /api/v1/invoices/43 are unknown.
- —All secondary pages (docs, API, pricing, README) render only 'Connect wallet' with no substantive content.
- —The specific purpose of the /api/v1/invoices/43 endpoint is unclear; 'Premium API Access' is a generic label that does not describe functionality.
- —Cannot verify what data or service is actually returned upon successful payment.
Citations
- —The endpoint returns a 402 challenge with x402 version 1, maxAmountRequired of 20000 base units USDC on Basehttps://lowpaymentfee.com/api/v1/invoices/43
- —All endpoints are priced at $0.02 per request with no API keys, no rate limits, and instant accesshttps://lowpaymentfee.com
- —The platform offers endpoints across Data & Analytics, AI & ML, Finance & Web3, and Infrastructure categorieshttps://lowpaymentfee.com
- —USDC contract address on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913https://lowpaymentfee.com/api/v1/invoices/43