Pay-per-call API platform on Base (USDC) offering data, AI, finance, and utility endpoints at $0.02/request.
What it does
lowpaymentfee.com is an x402-enabled API platform that provides a broad catalog of pay-per-request endpoints settled in USDC on the Base network. The specific endpoint `/api/v1/keys/21` is listed as "Premium API Access" and costs up to $0.02 per call (20,000 base units of USDC with 6 decimals). Payment is handled via the x402 protocol — no API keys, accounts, or subscriptions are required; callers attach an X-PAYMENT header with a signed USDC payment to each request.
The wider platform advertises 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 pricing. The platform claims no rate limits and instant access.
Important caveat: the specific functionality behind `/api/v1/keys/21` ("Premium API Access") is not documented beyond its title. There is no OpenAPI schema, no request/response examples, and the crawled docs and pricing pages returned only a wallet-connect prompt with no additional detail. The endpoint is confirmed live (returns a valid x402 402 challenge), but what it actually returns upon successful payment is unknown from available materials.
Capabilities
Use cases
- —Agents that need on-demand API access without managing API keys or subscriptions
- —Paying per-call for AI inference (sentiment, summarization, classification, embeddings)
- —Fetching real-time financial data (prices, exchange rates, gas estimates) with crypto micropayments
- —Geocoding or data validation without account setup
Fit
Best for
- —AI agents or bots that can sign x402 payments autonomously
- —Developers who want zero-signup, pay-as-you-go API access
- —Use cases requiring very low per-call costs ($0.02) with no minimum commitment
Not for
- —Users who need detailed API documentation or guaranteed SLAs before integrating
- —High-volume workloads where $0.02/request adds up and bulk pricing would be preferred
- —Callers who cannot transact in USDC on the Base network
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/keys/21 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <signed-x402-payment-header>"Endpoint
Quality
The endpoint is confirmed live via a valid x402 402 challenge, but there is no OpenAPI schema, no request/response examples, and no documentation explaining what /api/v1/keys/21 actually returns. The crawled pages beyond the homepage yielded only wallet-connect prompts. The listing is effectively a stub with pricing and liveness confirmed but functionality unknown.
Warnings
- —No documentation available for the specific endpoint /api/v1/keys/21 — its actual functionality is unknown
- —No OpenAPI or JSON schema describing request parameters or response format
- —Crawled /api, /pricing, and /README pages returned no useful content (only wallet-connect prompts)
- —The platform lists many endpoint categories but none have documented schemas or example payloads
Citations
- —The endpoint returns a valid x402 402 challenge with maxAmountRequired of 20000 base units of USDC on Basehttps://lowpaymentfee.com/api/v1/keys/21
- —USDC asset address 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913 on Base networkhttps://lowpaymentfee.com/api/v1/keys/21
- —All listed endpoints priced at $0.02 per request with no API keys, no rate limits, and instant accesshttps://lowpaymentfee.com
- —Platform offers Data & Analytics, AI & ML, Finance & Web3, and Infrastructure endpoint categorieshttps://lowpaymentfee.com