# createX402Fetch A drop-in `fetch` that pays for you. When a server answers `402 Payment Required`, it signs a payment with the agent's key and retries automatically. ```typescript import { createX402Fetch } from "@newton-xyz/isaac"; const fetch402 = createX402Fetch({ agentKey: "0x...", // agent private key rpcUrl: "https://sepolia.base.org", chainId: 84532, // optional, defaults to Base Sepolia }); ``` `createX402Fetch(config)` returns a fetch-like function. Have an agent's key held in a managed signing session instead of a raw key? Use `createX402FetchFromSigner({ signer, rpcUrl, chainId })`. ## Making a paid request ```typescript const result = await fetch402("https://api.example.com/data", { method: "GET", maxPayment: "1000000", // optional cap, in token base units }); if (result.success) { const data = await result.response.json(); console.log("paid", result.txHash, "on", result.network); } ``` The call takes the same options as `fetch`, plus `maxPayment` — the most the agent will pay in token base units (for example `"1000000"` is 1 USDC at 6 decimals). If the server asks for more, the request aborts and `result.success` is `false` without paying. A successful `result` carries the HTTP `response` and, when a payment was made, the settlement `txHash`, `network`, and `payer`. If the endpoint returns a normal (non-402) response, it comes straight back with no payment. ## See also * [Pay for an API](/guides/pay-for-an-api) — the full walkthrough. * [buildPolicyParams](/reference/sdk/build-policy-params) — cap what an agent is allowed to spend.