Pay-per-call API platform on Base (USDC) via x402 — data, AI, finance, and utility endpoints at $0.02/request.
What it does
lowpaymentfee.com is an x402-enabled API platform that offers a collection of endpoints spanning data & analytics, AI & machine learning, finance & Web3, and infrastructure utilities. All endpoints are pay-per-request using USDC on the Base network, settled via the x402 protocol. There are no API keys, no rate limits, and no minimum commitments — callers simply attach an X-PAYMENT header with a valid payment proof to access any endpoint.
The specific endpoint at `/api/v1/invoices/19` is listed as "Premium API Access" and requires a maximum of 20,000 base units of USDC (i.e., $0.02) per request. The platform advertises a uniform $0.02 per request across all its endpoints. Categories of available APIs include metrics, reports, data export, insights, sentiment analysis, text summarization, classification, embeddings, price feeds, exchange rates, token quotes, gas estimates, geocoding, validation, conversion, and generation.
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 usage examples available from the crawled material. The endpoint is confirmed live (returns a proper 402 x402 challenge), but without documentation it is unclear what request body format is expected or what the response payload looks like for this particular invoices endpoint.
Capabilities
Use cases
- —Accessing AI inference endpoints (sentiment, summarization, classification, embeddings) without API key registration
- —Fetching real-time finance data (prices, exchange rates, gas estimates) with per-call USDC payments
- —Running utility operations (geocoding, validation, conversion) on a pay-as-you-go basis
- —Integrating agent-purchasable API calls into autonomous workflows via x402
Fit
Best for
- —Developers wanting zero-signup, pay-per-use API access
- —AI agents that can settle payments autonomously via x402 on Base
- —Projects needing low-cost micropayment API calls at $0.02 each
Not for
- —Users who need detailed API documentation and request/response schemas before integrating
- —High-volume consumers who would benefit from bulk pricing or subscription plans
- —Developers without USDC on Base network
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/invoices/19 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-proof>"Endpoint
Quality
The endpoint is confirmed live with a valid x402 402 challenge, and the landing page lists available API categories with uniform pricing. However, documentation is effectively nonexistent — all doc/pricing/readme pages show only 'Connect wallet'. There is no OpenAPI spec, no request/response schemas, and no examples. The specific invoices/19 endpoint's purpose is unclear beyond the generic 'Premium API Access' label.
Warnings
- —Documentation pages (/docs, /api, /pricing, /README) all return only a 'Connect wallet' prompt with no technical content
- —No OpenAPI or schema documentation available for any endpoint
- —The purpose and expected input/output of /api/v1/invoices/19 specifically is undocumented
- —No request or response examples could be sourced from crawled material
- —It is unclear whether the advertised AI/data/finance endpoints are fully functional or placeholders
Citations
- —The endpoint returns a 402 x402 challenge with maxAmountRequired of 20000 base units of USDC on Basehttps://lowpaymentfee.com/api/v1/invoices/19
- —All endpoints are priced at $0.02 per request with no API keys, no rate limits, and instant accesshttps://lowpaymentfee.com
- —Available API categories include Data & Analytics, AI & Machine Learning, Finance & Web3, and Infrastructurehttps://lowpaymentfee.com
- —USDC asset address is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base networkhttps://lowpaymentfee.com/api/v1/invoices/19