> ## Documentation Index
> Fetch the complete documentation index at: https://docs.grain.inc/llms.txt
> Use this file to discover all available pages before exploring further.

# Overview

> Introduction to the Payment SDK — accept crypto payments in your application

## What is the Payment SDK?

The Payment SDK is a drop-in SDK that lets you accept cryptocurrency payments directly in your application. It handles wallet connections, network selection, transaction signing, and payment confirmation — so you can focus on your product.

The SDK renders inside a **Shadow DOM modal** for complete style isolation, supports multiple wallet providers, and works with any JavaScript framework.

```typescript theme={null}
// 1. Create a session on your server
const session = await fetch("/api/payment-sessions", {
  method: "POST",
  body: JSON.stringify({ amount: "50.00", currency: "USD" }),
});

// 2. Open the payment modal on the client
const transactionHash = await sdk.open({
  paymentSessionId: session.paymentSessionId,
  paymentSessionToken: session.paymentSessionToken,
});
```

## How It Works

<Steps>
  <Step title="Your server creates a payment session">
    Call the Grain API from your backend with the payment amount and currency. You receive a `paymentSessionId` and `paymentSessionToken`.
  </Step>

  <Step title="The SDK opens a payment modal">
    Pass the session credentials to the client-side SDK. It opens a modal where the customer selects a wallet, connects, and approves the transaction.
  </Step>

  <Step title="Customer funds a one-time wallet">
    Each session gets a unique one-time wallet (OTW) address. The customer's funds are sent to this address. The session status moves to `FUNDED`.
  </Step>

  <Step title="Your server captures the payment">
    Once funded, your server calls the capture endpoint to transfer funds from the OTW to your treasury wallet. You can capture the full amount or do partial captures.
  </Step>

  <Step title="You receive confirmation">
    The SDK returns the transaction hash on success. Your server receives webhooks as the session moves through `FUNDED` → `CAPTURING` → `SUCCEEDED`.
  </Step>
</Steps>

## Key Features

* **Drop-in modal** — Shadow DOM-based payment UI with full style isolation. No CSS conflicts with your application.
* **Multi-wallet support** — WalletConnect, injected wallets (MetaMask, Coinbase Wallet), and more out of the box.
* **Payment methods** — Crypto (stablecoins) with additional methods coming soon.
* **One-time wallets** — Every payment session gets a unique receiving address for clean reconciliation.
* **Flexible capture** — Capture the full amount or do partial captures. Final capture automatically refunds any remaining balance to the customer.
* **Webhook confirmations** — Receive server-side status updates via JSON-RPC 2.0 webhooks.
* **Customizable theme** — Match the payment modal to your brand with CSS custom properties.

## Payment Methods

| Method     | Description                                                     | Settlement |
| ---------- | --------------------------------------------------------------- | ---------- |
| **Crypto** | Customer pays with stablecoins (USDC) from any supported wallet | On-chain   |

## Next Steps

Get up and running in minutes. Follow the [Installation & Setup](/payment-sdk/installation-setup) guide to add the SDK to your project, then walk through the [Integration Guide](/payment-sdk/integration-guide/initialize-sdk) to process your first payment.