Pay gas in ERC20 tokens

Overview

This tutorial demonstrates how to use the Biconomy Smart Account to perform a transaction with ERC-20 token payment. The provided code includes creating a Biconomy Smart Account, encoding a function call, building a transaction, and sending it with ERC-20 token payment.

Prerequisites

• Node.js installed on your machine
• A Biconomy API key and Bundler url, get from dashboard

For this tutorial we are going to mint and NFT on Amoy, this means we can use the following:

• bundlerUrl --> https://bundler.biconomy.io/api/v2/80002/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44
• preferred ERC20 token for gas payment --> 0xf555F8d9Cf90f9d95D34488e6C852796D9acBd31 (USDC)
• nft address --> 0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e

Step 1: Create Biconomy Smart Account and Encode Function Call

const smartWallet = await createSmartAccountClient({
  signer, // can be viem client or ethers signer
  bundlerUrl,
  biconomyPaymasterApiKey,
});

const encodedCall = encodeFunctionData({
  abi: parseAbi(["function safeMint(address _to)"]),
  functionName: "safeMint",
  args: [recipient],
});

Create a Biconomy Smart Account instance and encode the function call for the transaction.

Step 2: Build the Transaction

const nftAddress = "0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e";
const transaction = {
  to: nftAddress,
  data: encodedCall,
};

Build the transaction with the encoded function call.

Step 3: Send Transaction with ERC-20 Preferred Token Payment

Preferred token

Pay the gas in your preferred token.

const { wait } = await smartWallet.sendTransaction(transaction, {
  paymasterServiceData: {
    mode: PaymasterMode.ERC20,
    preferredToken: "0xf555F8d9Cf90f9d95D34488e6C852796D9acBd31",
  },
});

const {
  receipt: { transactionHash },
  userOpHash,
  success,
} = await wait();

if(success == 'true') { 
  console.log("UserOp receipt", receipt)
  console.log("Transaction receipt", receipt.receipt)
}

List of tokens

You can choose from a list of ERC20 tokens to pay for the gas, not giving a preferred token will allow you to select from current supported tokens.

const feeQuotesResponse = await smartWallet.getTokenFees(transaction, {
  paymasterServiceData: { mode: PaymasterMode.ERC20 },
});

const userSelectedFeeQuote = feeQuotesResponse.feeQuotes?.[0]; // Allow user to pick desired token

const { wait } = await smartWallet.sendTransaction(transaction, {
  paymasterServiceData: {
    mode: PaymasterMode.ERC20,
    feeQuote: userSelectedFeeQuote,
    spender: feeQuotesResponse.tokenPaymasterAddress,
    maxApproval: true,
  },
});

const {
  receipt: { transactionHash },
  userOpHash,
  success,
} = await wait();

if(success == 'true') { 
  console.log("UserOp receipt", receipt)
  console.log("Transaction receipt", receipt.receipt)
}

Send the transaction using the Biconomy Smart Account, specifying ERC-20 token payment details. Wait for the transaction to be mined and get the transaction hash.

That's it! You've successfully performed a transaction with ERC-20 token payment using the Biconomy Smart Account. Feel free to customize this example based on your specific use case.