x402-gated premium API endpoint on Base, pay $0.02 per request in USDC.
What it does
This endpoint at `/api/v1/cards/51` is part of the lowpaymentfee.com platform, a collection of x402-protocol pay-per-request APIs spanning data analytics, AI/ML inference, finance/Web3, and infrastructure utilities. The specific `/api/v1/cards/51` resource is labeled "Premium API Access" but its exact functionality is not documented beyond that label — it is one of many endpoints on the platform, all priced uniformly at $0.02 per call.
Payment is handled via the x402 protocol on the Base network using USDC (contract `0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913`). The challenge advertises a `maxAmountRequired` of 20,000 base units, which at 6 decimals equals $0.02. No API keys or rate limits are required; callers simply attach an `X-PAYMENT` header with a valid x402 payment proof. The endpoint accepts HTTP POST and returns `application/json`.
The broader platform offers 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/request price point. However, documentation beyond the landing page is essentially empty (all sub-pages just show "Connect wallet"), so the actual request/response schemas for this and other endpoints are unknown.
Capabilities
Use cases
- —Accessing a premium data or utility endpoint with per-request USDC micropayments
- —Integrating x402-compatible agents that pay for API calls on the Base network
- —Testing x402 payment flows against a live endpoint
Fit
Best for
- —Developers experimenting with x402 pay-per-request protocols
- —Agents that need keyless, pay-as-you-go API access on Base
- —Low-cost micropayment API consumption without subscriptions
Not for
- —Users who need detailed API documentation or request/response schemas before integrating
- —High-volume use cases where per-request pricing may add up without volume discounts
- —Anyone without a Base-network USDC wallet
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/cards/51 \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-proof>"Endpoint
Quality
The endpoint is live and returns a valid x402 challenge with clear pricing, but there is no documentation of what this specific endpoint does, no request/response schema, and all doc pages are empty. The 'Premium API Access' label is generic and uninformative.
Warnings
- —The exact functionality of /api/v1/cards/51 is undocumented — 'Premium API Access' is the only description available.
- —All documentation pages (docs, api, pricing, README) return only 'Connect wallet' with no actual content.
- —No OpenAPI spec, no request schema, and no response schema are available.
- —The endpoint's purpose must be guessed; it could be a placeholder or test endpoint.
Citations
- —The platform lists APIs across data/analytics, AI/ML, finance/Web3, and infrastructure categories, all priced at $0.02/request.https://lowpaymentfee.com
- —The x402 challenge shows maxAmountRequired of 20000 base units in USDC on Base network.https://lowpaymentfee.com/api/v1/cards/51
- —USDC asset contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913.https://lowpaymentfee.com/api/v1/cards/51
- —No API keys, no rate limits, instant access advertised.https://lowpaymentfee.com