# 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.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.402gate.com/developer-integration/quick-start.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.