--- title: "Sandbox" description: "Test an x402 integration end to end against paid endpoints Superstables operates on Base Sepolia, with test USDC." canonical: "https://www.superstables.com/docs/sandbox" last-updated: 2026-10-04 --- # Sandbox On Base Sepolia, Superstables operates eleven paid endpoints for testing: demo market data at `/api/demo/market`, and ten prepared services under `/api/demo/services/` that return simulated output, marked as such. They are real x402 v2 sellers. Payments are test USDC on Base Sepolia (`eip155:84532`), scheme `exact`, settled through a public facilitator. No real money moves. ## Find them - [`/discovery/resources`](https://www.superstables.com/discovery/resources): the x402 discovery list, with each endpoint's exact payment terms. - [`/api/demo/catalogue`](https://www.superstables.com/api/demo/catalogue): each endpoint's parameters, allowed values and price. - [`/openapi.json`](https://www.superstables.com/openapi.json): the two API paths covering all eleven paid endpoints, with their `402` answers. ## Call one ```bash curl -i "https://www.superstables.com/api/demo/market?asset=BTC" ``` Unpaid, a valid request answers `402 Payment Required`. The `PAYMENT-REQUIRED` header carries the terms as base64-encoded JSON, and the body repeats them. Sign a payment for those terms and repeat the request with the signed payment payload in a `PAYMENT-SIGNATURE` header. After successful verification and settlement, the service returns `200` with the result and a `PAYMENT-RESPONSE` header describing the settlement. Parameters are checked first: an invalid request is a `400`, and nothing is demanded for it. ## Test USDC Get test USDC at https://faucet.circle.com (choose Base Sepolia). No ETH is needed: the facilitator pays the gas. ## With an owner's approval See the [HTTP purchase preview](https://www.superstables.com/docs/purchase.md) for payment requests and [Budgets on superstables.com](https://www.superstables.com/docs/budgets.md) for granting an agent a budget. **Testnet only.**