> ## Documentation Index
> Fetch the complete documentation index at: https://circle-devdocs-test-ai-codegen-component.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# How-to: Create a Unified USDC Balance

Circle Gateway allows you to establish a unified USDC balance consisting of USDC
stored on multiple source chains. Once established, you can transfer this
balance instantly to any destination chain.

This guide demonstrates how to establish a unified USDC balance by depositing
USDC into the Gateway Wallet contract. You can perform this action on multiple
chains to establish a chain-abstracted balance.

## Prerequisites

Before you begin, ensure that you've:

* Installed **Node.js** and **npm** on your development machine
* Created a testnet wallet on Ethereum Sepolia and have the private key
  available
* Funded your testnet wallet with USDC and native tokens
* Created a new Node project and have the following dependencies installed:
  * `viem`
  * `dotenv`
* You've set up a `.env` file with the following variables:

  ```text theme={null}
  PRIVATE_KEY=<your_private_key>
  ```

## Steps

Follow these steps to establish a unified USDC balance. Note that this example
demonstrates how to deposit USDC on a single chain (Ethereum Sepolia). Repeat
these steps on other chains to add to your balance.

### Step 1. Approve the Gateway Wallet to transfer USDC from your address

Create a new file called `index.js` in the root of your project, and add the
following code to it. This code calls the `approve()` method on the USDC
contract to allow the Gateway Wallet contract to transfer USDC from your wallet.

```javascript Javascript theme={null}
import "dotenv/config";
import { createPublicClient, getContract, http, erc20Abi } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import * as chains from "viem/chains";

// Partial ABI for the functions needed on the Gateway wallet
const gatewayWalletAbi = [
  {
    type: "function",
    name: "deposit",
    inputs: [
      {
        name: "token",
        type: "address",
        internalType: "address",
      },
      {
        name: "value",
        type: "uint256",
        internalType: "uint256",
      },
    ],
    outputs: [],
    stateMutability: "nonpayable",
  },
];

// Contract addresses on Ethereum Sepolia
const gatewayWalletAddress = "0x0077777d7EBA4688BDeF3E311b846F25870A19B9";
const usdcAddress = "0x1c7D4B196Cb0C7B01d743Fbc6116a902379C7238";

const DEPOSIT_AMOUNT = 10_000000n; // 10 USDC
const account = privateKeyToAccount(process.env.PRIVATE_KEY);

const client = createPublicClient({
  chain: chains["sepolia"],
  account,
  transport: http(),
});

const usdc = getContract({ address: usdcAddress, abi: erc20Abi, client });
const gatewayWallet = getContract({
  address: gatewayWalletAddress,
  abi: gatewayWalletAbi,
  client,
});

const approvalTx = await usdc.write.approve([
  gatewayWallet.address,
  DEPOSIT_AMOUNT,
]);

await client.waitForTransactionReceipt({ hash: approvalTx });
```

### Step 2. Call the deposit method on the Gateway Wallet contract

Add the following code to the `index.js` file to call the `deposit()` method on
the Gateway Wallet contract. Note that you must use the `deposit()` method and
not the standard transfer on the USDC contract.

<Warning>
  **Warning:** Directly transferring USDC to the Gateway Wallet contract with a
  standard ERC-20 transfer will result in loss of that USDC. You must use one of
  the deposit methods on the wallet contract to get a unified USDC balance.
</Warning>

```javascript Javascript theme={null}
const depositTx = await gatewayWallet.write.deposit([
  usdc.address,
  DEPOSIT_AMOUNT,
]);
```

### Step 3. Run the script

Once you have added the code to your `index.js` file, run it with the following
command:

```shell Shell theme={null}
node index.js
```

### Step 4. Wait for the required number of block confirmations

Wait for the
[required number of block confirmations](/gateway/references/supported-blockchains#required-block-confirmations).
Once the deposit transaction is final, your unified balance to reflects the
amount from Ethereum Sepolia. If you have balances on other chains, the total
balance is the sum of all the USDC from deposit transactions across all
supported chains that have reached finality.