x402-gated portfolio transactions endpoint on Base, pay-per-call with USDC.
What it does
This endpoint at lowpaymentfee.com exposes a POST-based portfolio transactions API at `/api/v1/portfolios/81/transactions`, gated by the x402 payment protocol. Each request costs up to $0.02 USDC (maxAmountRequired of 20,000 base units at 6 decimals) settled on the Base network. The endpoint accepts `application/json` and requires an `X-PAYMENT` header containing a valid x402 payment proof. No API keys or rate limits are advertised — access is granted purely through per-call micropayments.
The specific endpoint listed here is for portfolio ID 81's transactions. The broader lowpaymentfee.com platform advertises a wide catalog of x402-gated APIs spanning data analytics, AI/ML inference (sentiment, summarization, classification, embeddings), finance/crypto (price feeds, exchange rates, token quotes, gas estimates), and infrastructure utilities (geocoding, validation, conversion, generation), all at the same $0.02/request price point.
Documentation is extremely sparse. The docs, API, pricing, and README pages all render only a "Connect wallet" prompt with no further content. There is no OpenAPI schema, no request/response examples, and no description of what fields the transactions endpoint expects or returns. The endpoint is confirmed live (returns a proper 402 challenge), but without documentation it is difficult to know what payload to send or what data comes back.
Capabilities
Use cases
- —Submitting or retrieving transactions for a specific portfolio via micropayment
- —Integrating pay-per-call financial data into agent workflows
- —Testing x402 payment protocol integrations against a live endpoint
Fit
Best for
- —Developers experimenting with x402 micropayment protocol
- —Agents that need keyless, pay-per-call API access on Base
- —Low-volume or sporadic API consumers who want no subscriptions
Not for
- —Users needing detailed API documentation or schemas before integrating
- —High-volume batch processing where per-call fees add up
- —Anyone requiring non-crypto payment methods
Quick start
curl -X POST https://lowpaymentfee.com/api/v1/portfolios/81/transactions \
-H "Content-Type: application/json" \
-H "X-PAYMENT: <x402-payment-proof>" \
-d '{}'Endpoint
Quality
The endpoint is confirmed live with a valid 402 challenge and clear pricing ($0.02 USDC on Base). However, there is no OpenAPI schema, no request/response examples, and all documentation pages are empty beyond a wallet-connect prompt. The specific purpose of the portfolios/81/transactions endpoint is undocumented.
Warnings
- —No API documentation available — docs, pricing, and README pages all show only 'Connect wallet'
- —No OpenAPI or JSON schema describing request/response formats
- —The endpoint path includes a hardcoded portfolio ID (81); unclear if other IDs are accessible
- —Purpose and data model of 'transactions' endpoint is entirely undocumented
Citations
- —Endpoint returns 402 with x402 challenge, maxAmountRequired 20000 base units in USDC on Basehttps://lowpaymentfee.com/api/v1/portfolios/81/transactions
- —Platform advertises $0.02/request pricing with no API keys, no rate limits, and instant access on Base networkhttps://lowpaymentfee.com
- —USDC asset contract on Base: 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913https://lowpaymentfee.com/api/v1/portfolios/81/transactions