Token Transfers: EVM to Aptos

This tutorial demonstrates how to transfer tokens from an Ethereum Virtual Machine (EVM) chain to an Aptos wallet using Chainlink CCIP. You will learn how to build a CCIP message on an EVM chain, send it to the CCIP router, and verify the transfer on the destination chain.

Introduction

This tutorial covers transferring tokens from Ethereum Sepolia to an Aptos wallet without any additional data payload.

What You will Build

In this tutorial, you will:

  • Use a script to configure a CCIP message for a token-only transfer.
  • Send CCIP-BnM test tokens from Ethereum Sepolia to an Aptos wallet.
  • Pay for CCIP transaction fees using either native ETH or LINK tokens.
  • Monitor and verify your cross-chain transfer.

Understanding Token Transfers to Aptos

This tutorial focuses on token-only transfers from an EVM chain to an Aptos wallet.

Key points specific to token-only transfers to Aptos:

  • No Program Execution: Tokens are transferred directly to a wallet without executing a custom module.
  • Mandatory Settings:
    • The receiver field in the CCIP message must be the end user's Aptos wallet address.
    • The data field must be empty (0x).
    • The extraArgs field should be encoded with gasLimit: 0 and allowOutOfOrderExecution: true.

Implementing Token Transfers

In this section, you'll execute a token transfer from Ethereum Sepolia to Aptos Testnet using the example script located at scripts/evm2aptos/ccipSendTokenRouter.ts in the starter kit.

Token Transfer Configuration

The core of the transfer is configuring the EVM2AnyMessage correctly. The script handles this for you by calling a buildCCIPMessage function. Here's what the configuration looks like within the script:

// Inside the transferTokenPayNative function for example:
const ccipMessage = buildCCIPMessage(
  recipient, // Your Aptos wallet address from .env
  "0x", // Data is empty for a token-only transfer
  tokenAddress, // CCIP-BnM token address on Ethereum Sepolia
  tokenAmount, // The amount of tokens to send
  ethers.ZeroAddress, // For paying fees in native ETH
  encodeExtraArgsV2(0n, true) // gasLimit is 0, allowOutOfOrderExecution is true
)

How the Script Works

The evm2aptos/ccipSendTokenRouter.ts script automates the entire cross-chain transfer process. Based on your command-line arguments, it performs the following steps:

  1. Selects Chain Configuration: Selects the correct RPC URL and contract addresses for the Ethereum Sepolia testnet based on the --sourceChain sepolia argument.
  2. Builds the CCIP Message: Configures the message with the parameters shown above.
  3. Calculates Fees: Calls the getFee function on the source chain's Router to determine the required CCIP fee.
  4. Approves Tokens:
    • Approves the Router to spend the CCIP-BnM tokens you are transferring.
    • If paying with LINK, it also approves the Router to spend the required amount of LINK tokens for the fee.
  5. Executes Transfer: Calls the ccipSend function on the CCIP Router contract to initiate the cross-chain transfer, sending native tokens for the fee if specified.
  6. Returns Message ID: Parses the transaction receipt to find and display the CCIPMessageSent event and its unique messageId.

Running the Token Transfer

Prerequisites Check

  1. Ensure you've completed the setup steps outlined in the prerequisites.
  2. Make sure your .env file contains your PRIVATE_KEY (of your wallet on Ethereum Sepolia from which you're sending CCIP-BnM tokens) and ETHEREUM_SEPOLIA_RPC_URL.
  3. Verify you have sufficient native ETH and CCIP-BnM token balances in your EVM wallet on Ethereum Sepolia network.

Execute the Script

Run the following command from your terminal to transfer CCIP-BnM tokens from Ethereum Sepolia to Aptos Testnet, paying the fee in native ETH. You can change the value for the --amount flag to send a different number of tokens.

npx ts-node scripts/evm2aptos/ccipSendTokenRouter.ts --sourceChain sepolia --feeToken native --amount 0.001 --aptosReceiver <0x_YOUR_APTOS_WALLET_ADDRESS>

To pay with LINK instead, change the feeToken argument:

npx ts-node scripts/evm2aptos/ccipSendTokenRouter.ts --sourceChain sepolia --feeToken link --amount 0.001 --aptosReceiver <0x_YOUR_APTOS_WALLET_ADDRESS>

Understanding the Output

When the script executes successfully, you'll see output similar to this, showing the steps for a transfer from Ethereum Sepolia:

Base Fee (in WEI): 80690622338859
Fee with 20% buffer (in WEI): 96828746806630
Current Allowance of CCIP-BnM token: 0
Approval tx sent: 0x1a1fb6362f2eac4a6a52e4974e15fa071bc9084ad99273ef8aa5b37a9bc0568d
Approval transaction confirmed in block 8775988 after 3 confirmations.
Router contract approved to spend 1000000000000000 of CCIP-BnM token from your account.
Proceeding with the token transfer...
Transaction sent: 0x06d2657c1939f5cba4b29052977355a5cee131a6ffefe80550aeb80c383b9450
Waiting for transaction confirmation...
Transaction confirmed in block 8775991 after 3 confirmations.
✅ Transaction successful: https://sepolia.etherscan.io/tx/0x06d2657c1939f5cba4b29052977355a5cee131a6ffefe80550aeb80c383b9450
🆔 CCIP Message ID: 0x54d2e9fb4b7e852b30fae6617a568e729b714b5d658fa85592def65901b84c56
🔗 CCIP Explorer URL: https://ccip.chain.link/#/side-drawer/msg/0x54d2e9fb4b7e852b30fae6617a568e729b714b5d658fa85592def65901b84c56
  • The output displays the base fee and the fee with a 20% buffer, both shown in the smallest denomination of the fee token (i.e., WEI for the native token).
  • It checks the current allowance of the CCIP-BnM token and approves the Router contract to spend the specified amount if necessary.
  • The transaction hash is displayed, which you can use to track the transfer on Ethereum Sepolia.
  • The output provides the unique CCIP Message ID, which is essential for tracking your transfer.
  • The CCIP Explorer URL allows you to monitor the message status across chains.

Verification and Monitoring

After sending your token transfer, you can verify its arrival on Aptos in the following ways:

Check Message Execution

Use the CCIP Explorer to check the message status

Use the CCIP Explorer link provided in the transaction output to track your message status across chains. The explorer gives an overview of the entire cross-chain transaction life cycle.

🔗 CCIP Explorer URL: https://ccip.chain.link/#/side-drawer/msg/<YOUR_CCIP_MESSAGE_ID>

Programmatically check the message status

After you receive a CCIP Message ID, you can programmatically check if the CCIP message has been successfully executed on the Aptos network. This is done by querying the ExecutionStateChanged event emitted by the CCIP OffRamp module. The evm2aptos/checkMsgExecutionStateOnAptos.ts script is designed for this purpose.

After 15-20 minutes, run the script using the CCIP Message ID you received from the previous step.

Command:

npx ts-node scripts/evm2aptos/checkMsgExecutionStateOnAptos.ts --msgId <YOUR_CCIP_MESSAGE_ID>

Replace <YOUR_CCIP_MESSAGE_ID> with the actual CCIP Message ID from the log output.

Output: When the message has been successfully delivered, you will see the following output:

Execution state for CCIP message 0x54d2e9fb4b7e852b30fae6617a568e729b714b5d658fa85592def65901b84c56 is SUCCESS

Verify Token Balance

Once the script confirms a SUCCESS state, you can perform a final verification on a block explorer.

  • Visit the Aptos Explorer.
  • Search for your Aptos wallet address.
  • Under the "Coins" tab, you should see the balance of the CCIP-BnM token you transferred.

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