> For the complete documentation index, see [llms.txt](https://docs.402gate.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.402gate.com/developer-integration/quick-start.md).

# Quick Start

#### **Step 1: Install the SDK**

The 402Gate SDK makes integration with Solana seamless.

```bash
npm install @402gate/sdk
```

Or using Yarn:

```bash
yarn add @402gate/sdk
```

***

#### **Step 2: Import and Initialize**

Use the SDK in your app (Node.js, Next.js, or Express).

```js
import { create402Middleware } from "@402gate/sdk";

const middleware = create402Middleware({
  price: 0.001,
  token: "402G",
  recipient: "MERCHANT_PUBKEY",
  verifyOnChain: true
});
```

Attach it to your API route or service:

```js
app.use("/api/premium", middleware);
```

This automatically:

* Detects unpaid requests and responds with `HTTP 402 Payment Required`.
* Verifies on-chain proof of payment.
* Grants access once valid.

***

#### **Step 3: Handle Client Payment**

On the frontend or AI client side:

```js
import { fetchWith402 } from "@402gate/sdk/client";

const response = await fetchWith402("https://api.402gate.app/premium", {
  wallet: userWallet,
  tokens: ["402G", "USDC", "SOL"]
});
```

If the endpoint responds with `HTTP 402`, the SDK will automatically:

* Parse the payment metadata (amount, token, requestId).
* Prompt user/agent to sign the transaction.
* Retry the request after payment is confirmed.


---

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