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Version: SDK V3

Mint Your NFT on Multiple Chains with One Signature 🌍✍️

Transitioning to multichain opens up exciting possibilities.

In this guide, we'll start from scratch to enable minting an NFT on multiple chains, specifically Polygon Mumbai and Base test networks, using just one signature.

Supported Chains

Find all supported chains here. Our NFT contract has the same address on both Polygon and Base (0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e).

🛠️ Initial Setup​

Importing Required Modules​

Begin by importing the necessary modules for blockchain interaction and configuration.

import { config } from "dotenv";
import { IBundler, Bundler } from "@biconomy/bundler";
import { ChainId } from "@biconomy/core-types";
import {
  BiconomySmartAccountV2,
  DEFAULT_ENTRYPOINT_ADDRESS,
} from "@biconomy/account";
import {
  MultiChainValidationModule,
  DEFAULT_MULTICHAIN_MODULE,
} from "@biconomy/modules";
import { ethers } from "ethers";
import {
  IPaymaster,
  BiconomyPaymaster,
  PaymasterMode,
  SponsorUserOperationDto,
} from "@biconomy/paymaster";

Setting Up Ethereum Provider and Wallet​

Establish your Ethereum provider and wallet for interacting with the blockchain.

config();
const provider = new ethers.providers.JsonRpcProvider(
  "https://rpc.ankr.com/polygon_mumbai",
);
const wallet = new ethers.Wallet(process.env.PRIVATE_KEY || "", provider);

Configuring Bundler and Paymaster for Networks​

Configure the Bundler and Paymaster for both Polygon Mumbai and Base Goerli Testnet.

// Configure the Bundler and Paymaster for Polygon Mumbai network
const mumbaiBundler: IBundler = new Bundler({
  bundlerUrl:
    "https://bundler.biconomy.io/api/v2/80001/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44",
  chainId: ChainId.POLYGON_MUMBAI,
  entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS,
});

const mumbaiPaymaster: IPaymaster = new BiconomyPaymaster({
  paymasterUrl:
    "https://paymaster.biconomy.io/api/v1/80001/Tpk8nuCUd.70bd3a7f-a368-4e5a-af14-80c7f1fcda1a",
});

// Configure the Bundler and Paymaster for Base Goerli Testnet
const baseBundler = new Bundler({
  bundlerUrl:
    "https://bundler.biconomy.io/api/v2/84531/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44",
  chainId: ChainId.BASE_GOERLI_TESTNET,
  entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS,
});

const basePaymaster: IPaymaster = new BiconomyPaymaster({
  paymasterUrl:
    "https://paymaster.biconomy.io/api/v1/84531/m814QNmpW.fce62d8f-41a1-42d8-9f0d-2c65c10abe9a",
});

🌐 Creating Multichain Module​

Multichain Validation Module​

Create a Multichain Validation Module to enable cross-chain functionality.

async function createModule() {
  return await MultiChainValidationModule.create({
    signer: wallet,
    moduleAddress: DEFAULT_MULTICHAIN_MODULE,
  });
}

Smart Account Creation for Both Networks​

Generate Smart Accounts for Polygon Mumbai and Base Goerli Testnet using the Multichain Module.

// Function to create a smart account using the specified chain ID, bundler, and paymaster
async function createSmartAccount(
  chainId: ChainId,
  bundler: IBundler,
  paymaster: IPaymaster,
) {
  const module = await createModule();
  let smartAccount = await BiconomySmartAccountV2.create({
    chainId,
    paymaster,
    bundler,
    entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS,
    defaultValidationModule: module,
    activeValidationModule: module,
  });
  console.log(
    "Smart Account Address: ",
    await smartAccount.getAccountAddress(),
  );
  return smartAccount;
}
warning

🚨 Your Smart Account address is counterfactually generated based on the module and parameters used. When switching to multichain module, the address will change while deploying your Smart Account.

🌐 Minting NFTs on Multiple Networks​

The mintNFT function is the core of our multi-chain NFT minting process. Let's break it down to understand its functionality.

Creating Smart Accounts for Each Network 🛠️​

First, we create smart accounts for both networks. Each account is configured with its respective chain ID, bundler, and paymaster.

const mumbaiSmartAccount = await createSmartAccount(
  ChainId.POLYGON_MUMBAI,
  mumbaiBundler,
  mumbaiPaymaster,
);
const baseSmartAccount = await createSmartAccount(
  ChainId.BASE_GOERLI_TESTNET,
  baseBundler,
  basePaymaster,
);

Setting Up the NFT Contract Interface 📜​

Next, we define the NFT contract interface and encode the data for the safeMint function. This data is crucial for creating our NFT minting transaction.

const nftInterface = new ethers.utils.Interface([
  "function safeMint(address _to)",
]);
const data = nftInterface.encodeFunctionData("safeMint", [
  await baseSmartAccount.getAccountAddress(),
]);

Preparing Transactions for Each Network 📦​

For each network, we build a user operation (UserOp) for the minting transaction. These operations will later be signed and executed.

let partialUserOp = await mumbaiSmartAccount.buildUserOp(
  [{ to: nftAddress, data }],
  { paymasterServiceData: { mode: PaymasterMode.SPONSORED } },
);
let partialUserOp2 = await baseSmartAccount.buildUserOp(
  [{ to: nftAddress, data }],
  { paymasterServiceData: { mode: PaymasterMode.SPONSORED } },
);

Signing Operations for Both Networks ✍️​

Using the Multichain Module, we sign the operations for both networks. This step is crucial for validating our transactions across different blockchains.

const resolvedOps = await(await createModule()).signUserOps([
  { userOp: partialUserOp, chainId: ChainId.POLYGON_MUMBAI },
  { userOp: partialUserOp2, chainId: ChainId.BASE_GOERLI_TESTNET },
]);

Executing Transactions on Each Network 🚀​

Finally, we execute the signed operations on each network. The function waits for the transaction to complete and logs the transaction details for verification.

try {
  const userOpResponse1 = await mumbaiSmartAccount.sendSignedUserOp(
    resolvedOps[0],
  );
  const userOpResponse2 = await baseSmartAccount.sendSignedUserOp(
    resolvedOps[1],
  );

  const transactionDetails1 = await userOpResponse1.wait();
  const transactionDetails2 = await userOpResponse2.wait();
  console.log(
    "Polygon Mumbai Transaction: https://mumbai.polygonscan.com/tx/" +
      transactionDetails1.receipt.transactionHash,
  );
  console.log(
    "Base Goerli Transaction: https://goerli.basescan.org/tx/" +
      transactionDetails2.receipt.transactionHash,
  );
} catch (e) {
  console.log("Error:", e);
}

🚀 Launching the Mint Function​

Trigger the mintNFT function to start minting your NFTs on both networks.

mintNFT();
📝 Click to view the complete mintNFT function
async function mintNFT() {
  // Create smart accounts for both Polygon Mumbai and Base Goerli networks
  const mumbaiSmartAccount = await createSmartAccount(
    ChainId.POLYGON_MUMBAI,
    mumbaiBundler,
    mumbaiPaymaster,
  );
  const baseSmartAccount = await createSmartAccount(
    ChainId.BASE_GOERLI_TESTNET,
    baseBundler,
    basePaymaster,
  );

  // Define the interface for the NFT contract and encode data for the 'safeMint' function
  const nftInterface = new ethers.utils.Interface([
    "function safeMint(address _to)",
  ]);
  const data = nftInterface.encodeFunctionData("safeMint", [
    await baseSmartAccount.getAccountAddress(),
  ]);
  const nftAddress = "0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e";

  // Build user operations for the Polygon Mumbai network
  let partialUserOp = await mumbaiSmartAccount.buildUserOp(
    [{ to: nftAddress, data }],
    {
      paymasterServiceData: { mode: PaymasterMode.SPONSORED },
    },
  );

  // Build user operations for the Base Goerli network
  let partialUserOp2 = await baseSmartAccount.buildUserOp(
    [{ to: nftAddress, data }],
    {
      paymasterServiceData: { mode: PaymasterMode.SPONSORED },
    },
  );

  // Sign operations for both networks
  const resolvedOps = await (
    await createModule()
  ).signUserOps([
    { userOp: partialUserOp, chainId: ChainId.POLYGON_MUMBAI },
    { userOp: partialUserOp2, chainId: ChainId.BASE_GOERLI_TESTNET },
  ]);

  // Execute the operations on both networks and log the transaction details
  try {
    const userOpResponse1 = await mumbaiSmartAccount.sendSignedUserOp(
      resolvedOps[0],
    );
    const userOpResponse2 = await baseSmartAccount.sendSignedUserOp(
      resolvedOps[1],
    );

    const transactionDetails1 = await userOpResponse1.wait();
    const transactionDetails2 = await userOpResponse2.wait();
    console.log(
      "Polygon Mumbai Transaction: https://mumbai.polygonscan.com/tx/" +
        transactionDetails1.receipt.transactionHash,
    );
    console.log(
      "Base Goerli Transaction: https://goerli.basescan.org/tx/" +
        transactionDetails2.receipt.transactionHash,
    );
  } catch (e) {
    console.log("Error encountered: ", e);
  }
}
tip

Feel free to modify the mintNFT function as per your contract's requirements.

Through this setup, you've unlocked the potential to mint NFTs across multiple blockchains. With these capabilities, you can extend your reach across various networks. 🚀💡

📝 Click to view the complete
import { config } from "dotenv";
import { IBundler, Bundler } from "@biconomy/bundler";
import { ChainId } from "@biconomy/core-types";
import {
  BiconomySmartAccountV2,
  DEFAULT_ENTRYPOINT_ADDRESS,
} from "@biconomy/account";
import {
  MultiChainValidationModule,
  DEFAULT_MULTICHAIN_MODULE,
} from "@biconomy/modules";
import { ethers } from "ethers";
import {
  IPaymaster,
  BiconomyPaymaster,
  PaymasterMode,
  SponsorUserOperationDto,
} from "@biconomy/paymaster";

config();
const provider = new ethers.providers.JsonRpcProvider(
  "https://rpc.ankr.com/polygon_mumbai",
);
const wallet = new ethers.Wallet(process.env.PRIVATE_KEY || "", provider);

// Configure the Bundler and Paymaster for Polygon Mumbai network
const mumbaiBundler: IBundler = new Bundler({
  bundlerUrl:
    "https://bundler.biconomy.io/api/v2/80001/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44",
  chainId: ChainId.POLYGON_MUMBAI,
  entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS,
});

const mumbaiPaymaster: IPaymaster = new BiconomyPaymaster({
  paymasterUrl:
    "https://paymaster.biconomy.io/api/v1/80001/Tpk8nuCUd.70bd3a7f-a368-4e5a-af14-80c7f1fcda1a",
});

// Configure the Bundler and Paymaster for Base Goerli Testnet
const baseBundler = new Bundler({
  bundlerUrl:
    "https://bundler.biconomy.io/api/v2/84531/nJPK7B3ru.dd7f7861-190d-41bd-af80-6877f74b8f44",
  chainId: ChainId.BASE_GOERLI_TESTNET,
  entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS,
});

const basePaymaster: IPaymaster = new BiconomyPaymaster({
  paymasterUrl:
    "https://paymaster.biconomy.io/api/v1/84531/m814QNmpW.fce62d8f-41a1-42d8-9f0d-2c65c10abe9a",
});

async function createModule() {
  return await MultiChainValidationModule.create({
    signer: wallet,
    moduleAddress: DEFAULT_MULTICHAIN_MODULE,
  });
}

// Function to create a smart account using the specified chain ID, bundler, and paymaster
async function createSmartAccount(
  chainId: ChainId,
  bundler: IBundler,
  paymaster: IPaymaster,
) {
  const module = await createModule();
  let smartAccount = await BiconomySmartAccountV2.create({
    chainId,
    paymaster,
    bundler,
    entryPointAddress: DEFAULT_ENTRYPOINT_ADDRESS,
    defaultValidationModule: module,
    activeValidationModule: module,
  });
  console.log(
    "Smart Account Address: ",
    await smartAccount.getAccountAddress(),
  );
  return smartAccount;
}

async function mintNFT() {
  // Create smart accounts for both Polygon Mumbai and Base Goerli networks
  const mumbaiSmartAccount = await createSmartAccount(
    ChainId.POLYGON_MUMBAI,
    mumbaiBundler,
    mumbaiPaymaster,
  );
  const baseSmartAccount = await createSmartAccount(
    ChainId.BASE_GOERLI_TESTNET,
    baseBundler,
    basePaymaster,
  );

  // Define the interface for the NFT contract and encode data for the 'safeMint' function
  const nftInterface = new ethers.utils.Interface([
    "function safeMint(address _to)",
  ]);
  const data = nftInterface.encodeFunctionData("safeMint", [
    await baseSmartAccount.getAccountAddress(),
  ]);
  const nftAddress = "0x1758f42Af7026fBbB559Dc60EcE0De3ef81f665e";

  // Build user operations for the Polygon Mumbai network
  let partialUserOp = await mumbaiSmartAccount.buildUserOp(
    [{ to: nftAddress, data }],
    {
      paymasterServiceData: { mode: PaymasterMode.SPONSORED },
    },
  );

  // Build user operations for the Base Goerli network
  let partialUserOp2 = await baseSmartAccount.buildUserOp(
    [{ to: nftAddress, data }],
    {
      paymasterServiceData: { mode: PaymasterMode.SPONSORED },
    },
  );

  // Sign operations for both networks
  const resolvedOps = await (
    await createModule()
  ).signUserOps([
    { userOp: partialUserOp, chainId: ChainId.POLYGON_MUMBAI },
    { userOp: partialUserOp2, chainId: ChainId.BASE_GOERLI_TESTNET },
  ]);

  // Execute the operations on both networks and log the transaction details
  try {
    const userOpResponse1 = await mumbaiSmartAccount.sendSignedUserOp(
      resolvedOps[0],
    );
    const userOpResponse2 = await baseSmartAccount.sendSignedUserOp(
      resolvedOps[1],
    );

    const transactionDetails1 = await userOpResponse1.wait();
    const transactionDetails2 = await userOpResponse2.wait();
    console.log(
      "Polygon Mumbai Transaction: https://mumbai.polygonscan.com/tx/" +
        transactionDetails1.receipt.transactionHash,
    );
    console.log(
      "Base Goerli Transaction: https://goerli.basescan.org/tx/" +
        transactionDetails2.receipt.transactionHash,
    );
  } catch (e) {
    console.log("Error encountered: ", e);
  }
}

mintNFT();

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