# Quickstart for agents

> Make a paid call to an x402-gated endpoint from a Node script in 30 lines.

This guide walks through making an x402 paid call from an autonomous agent — a script, an LLM agent, or a browser tab. By the end you will have a Node script that pays a tiny amount of DEMO-USDT for a gated API response, with gas sponsored by the paymaster.

The complete runnable version of this script lives in the repo at [`examples/learn-nero/`](https://github.com/nerochain/nero-x402/tree/main/examples/learn-nero).

## Prerequisites

- An EOA private key. Generate one with `openssl rand -hex 32`. The corresponding SCW is derived deterministically from this key plus the canonical SimpleAccount factory.
- A NERO Paymaster API key from the [NERO AA Platform dashboard](https://docs.nerochain.io/en/developer-tools/aa-platform).
- The packages installed (see [Installation](/docs/getting-started/installation)).

The agent's SCW does **not** need a NERO native balance. The paymaster sponsors gas. On testnet the SCW does not even need DEMO-USDT to start — the script auto-mints from a public `mint()` on first run.

## The minimal flow

```ts
import { ethers } from "ethers";
import { x402Fetch, readSettlementReceipt } from "@nerochain/x402-client";
import { aaNativeSigner } from "@nerochain/x402-aa";

const wallet = new ethers.Wallet(process.env.NERO_PRIVATE_KEY!);

const f = x402Fetch({
  signer: aaNativeSigner({
    signer: wallet,
    rpcUrl:           "https://rpc-testnet.nerochain.io",
    bundlerUrl:       "https://bundler-testnet.nerochain.io",
    paymasterUrl:     "https://paymaster-testnet.nerochain.io",
    paymasterApiKey:  process.env.NERO_PAYMASTER_API_KEY!,
    settlementContract: "0x925dbba44570683ac8da99be08bc5ece8cf5a8c6",
  }),
});

const res = await f("http://localhost:4000/api/nero-knowledge", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({ question: "How does the paymaster work?" }),
});

console.log(res.status, await res.json());

const receipt = readSettlementReceipt(res);
if (receipt) {
  console.log("settled:", receipt.transactionHash);
  console.log("paid   :", ethers.formatUnits(receipt.amount, 6), "DEMO-USDT");
}
```

That is the entire payment loop. `x402Fetch` is a `fetch`-API-compatible function that:

1. Issues the request.
2. If it receives a 402 with a `PAYMENT-REQUIRED` header, asks the signer to construct a paymaster-sponsored UserOp targeting the settlement contract.
3. Re-issues the request with the signed payload in the `PAYMENT-SIGNATURE` header.
4. Returns the eventual 200 response with a `PAYMENT-RESPONSE` header that decodes to a structured settlement receipt.

## What happens behind the scenes

| Step | What runs | Where |
|---|---|---|
| Request 1 | Plain `fetch` | Agent → merchant |
| 402 response | Merchant middleware emits `PAYMENT-REQUIRED` | Merchant |
| Sign UserOp | `aaNativeSigner` builds + sponsors + signs the UserOp | Agent (in-process) |
| Request 2 | `fetch` with `PAYMENT-SIGNATURE` | Agent → merchant |
| `/verify` | Merchant middleware forwards to facilitator | Merchant → facilitator |
| `/settle` | Facilitator submits via bundler | Facilitator → bundler → chain |
| 200 response | Merchant attaches `PAYMENT-RESPONSE` (settlement receipt) | Merchant → agent |

The agent never sees the bundler or the facilitator directly. They are merchant-side concerns; the agent only signs the UserOp and re-issues the HTTP request.

## Pointing at mainnet

Swap the testnet URLs and contract for their mainnet equivalents:

```ts
rpcUrl:           "https://rpc.nerochain.io",
bundlerUrl:       "https://bundler-mainnet.nerochain.io",
paymasterUrl:     "https://paymaster-mainnet.nerochain.io",
settlementContract: "0x5eCfc64f2339992668f555918674B604F97B412D",
```

Mainnet has no auto-mint. Send real USDT to the SCW address before running. The SCW address is deterministic; the script in `examples/learn-nero/` prints it so you know where to fund.

## Next

- [Quickstart for merchants](/docs/getting-started/merchants) — the other side of the same flow.
- [SDK overview](/docs/sdk/overview) — the five packages, when to use which.
- [Whitepaper](/whitepaper.pdf) — the protocol's normative specification.