# Execute a Cross Chain Swap

This section explains the integration and usage of bridge protocols for cross-chain swapping functionalities.

<figure><img src="https://680235803-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FaWFVt3vE2Ci7ngiL0xHe%2Fuploads%2FEiAYuF6WJxpuIdaURBt1%2Fdiagram-export-11-23-2023-12_52_10-PM.png?alt=media&#x26;token=d56b1f70-2ca8-4ad9-aabd-7d72fc20f45f" alt="" width="563"><figcaption></figcaption></figure>

### Step 1: **Check the Allowance of the Bridge on the Token Contract**

To initiate a swap, first determine if the Bridge has the necessary allowance to access the tokens. This can be done using the following API endpoint:&#x20;

**API URL**: [`https://api.expand.network/fungibletoken/getuserallowance`](https://docs.expand.network/categories/fungible-tokens/erc20#getuserallowance)

***

**Sample Request:**

```url
https://api.expand.network/fungibletoken/getuserallowance?owner=0x6Fb447Ae94F5180254D436A693907a1f57696900&tokenAddress=0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2&spender=0xBA12222222228d8Ba445958a75a0704d566BF2C8
```

***

**Sample Response:**&#x20;

```json
{
    "status": 200,
    "msg": "success",
    "data": {
        "allowance": "999000000000000000000"
    }
}
```

### Step 2: Approve the Bridge from the Token Contract

If the allowance is less than the token amount to be swapped, the user must approve the Bridge contract from the token contract. \
This can be done using the following API endpoint:&#x20;

**API URL**: [`https://api.expand.network/fungibletoken/approve`](https://docs.expand.network/categories/fungible-tokens/erc20#approve)

***

**Sample Request:**

```json
{
    "from": "0x6Fb447Ae94F5180254D436A693907a1f57696900", 
    "tokenAddress":"0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",  
    "amount": "1000000000000000000000",                  
    "to": "0x6Fb447Ae94F5180254D436A693907a1f57696900", 
    "gas": "100000",
    "chainId": "1"
}
```

***

**Sample Response:**&#x20;

```json
{
    "status": 200,
    "msg": "success",
    "data": {
        "from": "0x6Fb447Ae94F5180254D436A693907a1f57696900",
        "to": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
        "value": "0",
        "gas": "100000",
        "data": "0x095ea7b3000000000000000000000000828b154032950c8ff7cf8085d841723db269605600000000000000000000000000000000000000000000003635c9adc5dea00000"
    }
}
```

### Step 3: Swap the tokens&#x20;

After the successful approval, we can do the swap. User can swap the tokens on their preferred Bridge by changing the "[bridgeId](https://docs.expand.network/ids/bridge-ids)" parameter.\
This can be done using the following API endpoint:&#x20;

**API URL**: [`https://api.expand.network/bridge/swap`](https://docs.expand.network/categories/bridge/stargate#swap)

***

**Sample Request:**

```json
{
    "bridgeId": "200",
    "srcChainId": "1",
    "dstChainId": "137",
    "srcTokenSymbol": "WETH",
    "dstTokenSymbol": "USDC",
    "amountIn": "100000000000000",
    "from": "0x6Fb447Ae94F5180254D436A693907a1f57696900",
    "gas": "920000",
    "to": "0x6Fb447Ae94F5180254D436A693907a1f57696900"
}
```

***

**Sample Response:**&#x20;

```json
{
    "status": 200,
    "msg": "success",
    "data": {
        "from": "0x6Fb447Ae94F5180254D436A693907a1f57696900",
        "to": "0xce16F69375520ab01377ce7B88f5BA8C48F8D666",
        "value": "83660648338674",
        "gas": "920000",
        "data": "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"
    }
}
```