x402-gated card-transaction endpoint on Base, pay-per-call with USDC.
What it does
This endpoint at lowpaymentfee.com exposes a card transactions resource at `/api/v1/cards/41/transactions` behind an x402 paywall. It accepts POST requests and settles payments in USDC on the Base network. The x402 challenge advertises a maximum cost of 20,000 base units of USDC (6 decimals), which equals $0.02 per request. No API keys or rate limits are required — callers simply attach an X-PAYMENT header with a valid x402 payment proof.
The broader lowpaymentfee.com platform lists numerous additional endpoints across data/analytics, AI/ML (sentiment analysis, summarization, classification, embeddings), finance/Web3 (price feeds, exchange rates, token quotes, gas estimates), and infrastructure utilities (geocoding, validation, conversion, generation), all at the same $0.02/request price point. However, this specific listing covers only the `/api/v1/cards/41/transactions` endpoint.
Documentation is extremely sparse. The crawled /docs, /api, /pricing, and /README pages all returned only a "Connect wallet" prompt with no substantive content. There is no OpenAPI schema, no request/response examples, and no description of what the "cards/41/transactions" resource actually returns or what POST body it expects. The endpoint is live (returns a well-formed 402 challenge), but its actual functionality and data model remain unclear.
Capabilities
Use cases
- —Retrieving or creating card transaction records via a pay-per-call model
- —Integrating card transaction data into agent workflows without API key management
- —Programmatic access to card transaction information settled in USDC on Base
Fit
Best for
- —Agents that need card transaction data with zero-signup access
- —Developers wanting to test x402 payment flows on Base
- —Use cases requiring per-request billing with no subscription commitment
Not for
- —Users who need detailed API documentation or schema guarantees before integrating
- —High-volume use cases where per-request pricing at $0.02 may be costly
- —Anyone needing clarity on what data fields are returned before paying
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/cards/41/transactions \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402_payment_proof>"Endpoint
Quality
The endpoint is live and returns a valid x402 challenge, but there is no documentation, no OpenAPI schema, no request/response examples, and no explanation of what 'cards/41/transactions' actually does. The listing is effectively a stub with only pricing and network information available.
Warnings
- —No documentation available — /docs, /api, /pricing, and /README pages all return only a wallet-connect prompt with no content
- —No OpenAPI or request/response schema provided; the POST body format and response structure are completely unknown
- —The purpose of 'cards/41/transactions' is unclear — it could be financial card data, gift cards, or something else entirely
- —The broader site lists many endpoints but none have documented schemas or examples
Citations
- —The endpoint returns a valid x402 challenge with maxAmountRequired of 20000 base units of USDC on Basehttps://lowpaymentfee.com/api/v1/cards/41/transactions
- —USDC asset contract on Base is 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913https://lowpaymentfee.com/api/v1/cards/41/transactions
- —All endpoints priced at $0.02/request with no API keys, no rate limits, and instant access on Base networkhttps://lowpaymentfee.com
- —The /docs, /api, /pricing, and /README pages contain only a 'Connect wallet' prompthttps://lowpaymentfee.com/docs