x402-gated premium API access on Base, pay $0.02 per request in USDC — no keys, no rate limits.
What it does
lowpaymentfee.com is a pay-per-call API platform that uses the x402 protocol to gate access to a variety of endpoints spanning data analytics, AI/ML inference, finance/Web3 data, and infrastructure utilities. Every request costs $0.02 in USDC on the Base network, settled directly on-chain with no API keys, subscriptions, or rate limits required.
The specific endpoint at `/api/v1/invoices/39` is listed as "Premium API Access" and returns an x402 challenge requesting up to 20,000 base units of USDC (0x8335…2913 on Base, 6 decimals → $0.02) via the "exact" payment scheme. The platform advertises sibling endpoints for metrics, reports, data export, insights, sentiment analysis, text summarization, classification, embeddings, price feeds, exchange rates, token quotes, gas estimates, geocoding, validation, conversion, and generation — all at the same $0.02 price point.
Documentation is extremely sparse: the /docs, /api, /pricing, and /README pages all render only a "Connect wallet" prompt with no further technical detail. There is no OpenAPI spec, no request/response schema documentation, and no example payloads available. The endpoint is confirmed live (402 challenge captured), but without documentation it is unclear what request body this particular invoice endpoint expects or what response it returns.
Capabilities
Use cases
- —Accessing AI inference endpoints (sentiment, summarization, classification, embeddings) without managing API keys
- —Fetching real-time financial data and crypto gas estimates with per-call USDC payments
- —Running geocoding or data conversion utilities on a pay-as-you-go basis
- —Programmatic agents purchasing API calls autonomously via x402 protocol
Fit
Best for
- —Developers who want zero-signup, pay-per-use API access
- —AI agents that can settle payments on Base via x402
- —Users who prefer on-chain micropayments over subscription billing
Not for
- —Users needing detailed API documentation or guaranteed SLAs before integrating
- —High-volume consumers who would benefit from bulk pricing or rate-limited tiers
- —Anyone without a Base-compatible USDC wallet
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/invoices/39 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-token>" \
-d '{}'Endpoint
Quality
The endpoint is confirmed live with a valid x402 402 challenge, and the landing page lists available endpoints with pricing. However, there is no OpenAPI spec, no request/response schema, no documentation beyond a wallet-connect prompt, and no examples. The specific purpose of /api/v1/invoices/39 is unclear beyond the generic 'Premium API Access' label.
Warnings
- —No OpenAPI or schema documentation available — request/response formats are unknown
- —All documentation pages (/docs, /api, /pricing, /README) render only 'Connect wallet' with no content
- —The specific function of /api/v1/invoices/39 is undocumented; it may be a generic or placeholder endpoint
- —No examples or error codes documented anywhere
Citations
- —The endpoint returns a 402 challenge requesting up to 20,000 base units of USDC on Base (asset 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913)https://lowpaymentfee.com/api/v1/invoices/39
- —All listed endpoints cost $0.02 per request with no API keys, no rate limits, and instant access on the Base networkhttps://lowpaymentfee.com
- —The platform offers endpoints across Data & Analytics, AI & Machine Learning, Finance & Web3, and Infrastructure categorieshttps://lowpaymentfee.com
- —Documentation pages (/docs, /api, /pricing, /README) show only a 'Connect wallet' prompthttps://lowpaymentfee.com/docs