Pay-per-call invoice API on Base via x402 — $0.02/request in USDC, no API keys required.
What it does
lowpaymentfee.com hosts a collection of pay-per-request APIs accessible via the x402 protocol on the Base network. The specific endpoint `/api/v1/invoices/30` is labeled "Premium API Access" and accepts POST requests. Payment is settled in USDC (contract 0x8335…2913 on Base) using the x402 "exact" scheme. The maximum amount required per call is 20,000 base units of USDC, which at 6 decimals equals $0.02 USD per request.
The broader lowpaymentfee.com platform advertises 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 listed at the same $0.02/request price point. The platform advertises no API keys, no rate limits, and instant access.
Documentation is extremely sparse — the /docs, /api, /pricing, 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 detailed documentation for what the `/api/v1/invoices/30` endpoint actually returns. The x402 challenge confirms the endpoint is live and accepting payment challenges, but the actual functionality behind this specific invoice endpoint is unclear from available materials.
Capabilities
Use cases
- —Programmatic access to invoice data with per-request USDC micropayments
- —Agent-driven API consumption without pre-registration or API keys
- —Integrating pay-as-you-go endpoints into automated workflows on Base
Fit
Best for
- —Developers wanting zero-signup, pay-per-call API access
- —AI agents that can settle x402 payments in USDC on Base
- —Projects needing low-friction micropayment-gated endpoints
Not for
- —Users who need detailed API documentation or OpenAPI specs before integrating
- —Applications requiring free or subscription-based access models
- —Use cases needing high-throughput with predictable flat-rate pricing
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/invoices/30 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-token>"Endpoint
Quality
The x402 challenge is live and confirms pricing and payment details, but there is zero documentation for this specific endpoint — no request schema, no response schema, no examples. The /docs and other pages are empty beyond a wallet connect prompt. The actual functionality of /api/v1/invoices/30 is unknown.
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 for this endpoint
- —The specific purpose and output of /api/v1/invoices/30 ('Premium API Access') is not described anywhere in crawled materials
- —No agents.txt or robots.txt present
Citations
- —The endpoint returns a 402 challenge with maxAmountRequired of 20000 base units of USDC on Basehttps://lowpaymentfee.com/api/v1/invoices/30
- —All endpoints are priced at $0.02/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 asset contract is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base networkhttps://lowpaymentfee.com/api/v1/invoices/30