> ## Documentation Index
> Fetch the complete documentation index at: https://anypay-docs-update-resources-2026-06-29.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Cross-Chain Execution

> Overview of cross-chain execution capabilities, transaction routing, and multi-blockchain coordination mechanisms

## Overview

Trails doesn't just move tokens cross-chain—it can execute arbitrary smart contract functions on the destination chain as part of the same transaction flow. This enables powerful use cases like cross-chain NFT mints, DeFi deposits, and protocol interactions.

## How It Works

When you include `to.calldata` in your Trails transaction, the protocol:

1. **Routes funds** from the user's selected source chain/token
2. **Bridges and swaps** as needed to the destination chain/token
3. **Executes your calldata** on the destination contract with the funds attached

All of this happens atomically from the user's perspective—one confirmation, one transaction.

## Example: Cross-Chain NFT Mint

A user on Arbitrum wants to mint an NFT on Base that costs 0.01 ETH. They only have USDC:

```tsx theme={null}
import { Pay } from '0xtrails/widget'
import { encodeFunctionData } from 'viem'

const mintCalldata = encodeFunctionData({
  abi: [{
    name: 'mint',
    type: 'function',
    stateMutability: 'payable',
    inputs: [{ name: 'to', type: 'address' }],
    outputs: [],
  }],
  functionName: 'mint',
  args: ['0xUserAddress'],
})

<Pay
  apiKey="YOUR_API_KEY"
  to={{
    recipient: "0xNFTContract",
    currency: "ETH",
    chain: "base",
    amount: "0.01",
    calldata: mintCalldata,
  }}
>
  <button>Mint NFT</button>
</Pay>
```

**What happens:**

1. User confirms a single transaction on Arbitrum
2. Trails swaps USDC → ETH and bridges to Base
3. On Base, Trails calls `mint()` on the NFT contract with 0.01 ETH attached
4. User receives their NFT

## Example: Cross-Chain DeFi Deposit

Deposit into an Aave lending pool on Arbitrum using tokens from any chain:

```tsx theme={null}
import { Fund } from '0xtrails/widget'
import { TRAILS_ROUTER_PLACEHOLDER_AMOUNT } from '0xtrails'
import { encodeFunctionData } from 'viem'

const supplyCalldata = encodeFunctionData({
  abi: [{
    name: 'supply',
    type: 'function',
    stateMutability: 'nonpayable',
    inputs: [
      { name: 'asset', type: 'address' },
      { name: 'amount', type: 'uint256' },
      { name: 'onBehalfOf', type: 'address' },
      { name: 'referralCode', type: 'uint16' },
    ],
    outputs: [],
  }],
  functionName: 'supply',
  args: [
    '0xUSDCAddress',
    TRAILS_ROUTER_PLACEHOLDER_AMOUNT, // Replaced with actual amount at execution
    '0xUserAddress',
    0,
  ],
})

<Fund
  apiKey="YOUR_API_KEY"
  to={{
    recipient: "0xAavePool",
    currency: "USDC",
    chain: "arbitrum",
    calldata: supplyCalldata,
  }}
>
  <button>Deposit to Aave</button>
</Fund>
```

## Supported Calldata Patterns

### Static Calldata

When the function parameters are known in advance:

* NFT mints with fixed recipient
* Staking with fixed parameters
* Any function where amount isn't a parameter

### Dynamic Calldata

When the amount needs to be determined at execution time, use `TRAILS_ROUTER_PLACEHOLDER_AMOUNT`:

* ERC-4626 vault deposits
* Lending protocol supplies
* Any function with an `amount` parameter that should match bridged funds

## Key Benefits

* **Single Transaction**: Users confirm once, regardless of complexity
* **Any Token → Any Function**: Pay with USDC, execute with ETH
* **Atomic Execution**: Calldata executes only if funds arrive successfully
* **No Contract Changes**: Works with existing smart contracts

## Use Cases

| Use Case             | Example                                 |
| -------------------- | --------------------------------------- |
| **NFT Minting**      | Mint on any chain with any token        |
| **DeFi Deposits**    | Supply to lending protocols cross-chain |
| **Staking**          | Stake tokens on any chain               |
| **Gaming**           | Purchase in-game items across chains    |
| **DAO Interactions** | Vote or participate with any token      |

## See Also

* [Pay Mode](/sdk/modes/pay) - Configuration for payment with calldata
* [Fund Mode](/sdk/modes/fund) - Configuration for deposits with calldata
* [How It Works](/architecture/how-it-works) - Detailed protocol architecture