# Pay for an API When an agent calls an endpoint that charges for access, the SDK handles the payment for you. The agent gets its data; you set the limit. ## How it works 1. Your agent requests a paid endpoint. 2. The server replies "payment required," with a price. 3. The SDK pays — if it's within the agent's budget — and retries the request. 4. The agent gets the response. If the price is over your per-call ceiling or the agent's daily limit, nothing is paid. ## Code ```typescript import { createX402Fetch } from "@newton-xyz/isaac"; const fetch402 = createX402Fetch({ agentKey: process.env.AGENT_KEY!, rpcUrl: process.env.RPC_URL!, }); const result = await fetch402("https://api.example.com/data", { method: "GET", maxPayment: "1000000", // 1 USDC ceiling for this call }); if (result.success) { const data = await result.response.json(); console.log("got data — paid in tx", result.txHash); } else { console.log("not paid:", result); // over budget, or denied by policy } ``` The agent needs a funded vault and a budget first — see [Give an Agent a Budget](/guides/agent-budget). ## Next * **[Issue a Card](/guides/issue-a-card)** — give an agent a virtual card. * **[Meter Your API](/guides/meter-your-api)** — charge agents to call your own API.