Pay with ERC20

This page details the process of paying the gas of user operations (UserOps) using ERC20 tokens.

ERC20 token payments are currently restricted to testnets as part of our staging environment. For this functionality, please use staging Gelato Bundler RPC as bundler transport.

Zerodev ERC20 Paymaster currently supports USDC on Ethereum Mainnet, Polygon, Base, Optimism, and Arbitrum networks, including both their mainnet and testnet environments. Learn more.

After reading this page:

• You'll know how to pay gas for UserOps using ERC20 tokens.

• You'll learn about how to use Zerodev Kernel and Safe as an smart account to pay gas.

• You'll see some code which will help you send a Non-Sponsored UserOp within minutes.

Initial Setup

1. Create Your ZeroDev Account

Register on the ZeroDev dashboard to access the tools necessary for managing and sponsoring gas fees in your projects.

2. Create a Project for a Specific Network

After signing in, create a new project and choose the network you plan to operate on (e.g., Ethereum, Polygon). This ensures that all settings and configurations match your target chain.

3. Retrieve the Paymaster URL

Within your project’s dashboard, locate and copy the Paymaster URL. This endpoint is essential for integrating the sponsorship service into your application. If you want custom ERC20 tokens for gas fees checkout here.

Example Code

1. Create an account using createKernelAccount from @zerodev/sdk

const entryPoint = getEntryPoint("0.7");
const kernelVersion = KERNEL_V3_1;

const ecdsaValidator = await signerToEcdsaValidator(publicClient, {
    signer,
    entryPoint,
    kernelVersion,
});

const account = await createKernelAccount(publicClient, {
    plugins: {
      sudo: ecdsaValidator,
    },
    entryPoint,
    kernelVersion
});

2. Create paymaster client using createZeroDevPaymasterClient

const zerodevPaymaster = createZeroDevPaymasterClient({
    chain: baseSepolia,
    transport: http(PAYMASTER_RPC), // from Zerodev Dashboard
});

3. Create an Client using createKernelAccountClient adding Gelato Bundler RPC with Zerodev paymaster

When using the Gelato Bundler with a ZeroDev Paymaster, you need to specify a specialized gas estimation method when creating the kernelClient. The Paymaster, along with its paymasterContext, is required for paying gas in ERC20 tokens—be sure to include the specific token address in the paymasterContext.

const gasPrices = await bundlerClient.request<EthGetUserOperationGasPriceRpc>({
            method: "eth_getUserOperationGasPrice",
            params: [],
});
const maxFeePerGas = BigInt(gasPrices.maxFeePerGas),
const maxPriorityFeePerGas = BigInt(gasPrices.maxPriorityFeePerGas),

const kernelClient = createKernelAccountClient({
    account,
    chain,
    bundlerTransport: http(process.env.BUNDLER_RPC),
    paymaster: paymasterClient,
    paymasterContext: {
      token: gasTokenAddresses[sepolia.id]["USDC"], // Setting ERC-20 token for gas fees
    },
    // Custom gas estimation for integrating Gelato Bundler with the ZeroDev SDK
    userOperation: {
      estimateFeesPerGas: async ({ bundlerClient }) => {
        const gasPrices =
          await bundlerClient.request<EthGetUserOperationGasPriceRpc>({
            method: "eth_getUserOperationGasPrice",
            params: [],
          });
        return {
          maxFeePerGas: BigInt(gasPrices.maxFeePerGas),
          maxPriorityFeePerGas: BigInt(gasPrices.maxPriorityFeePerGas),
        };
      },
    },
  });

Gas Config Types

type GasPrices = {
  maxFeePerGas: string;
  maxPriorityFeePerGas: string;
};

type EthGetUserOperationGasPriceRpc = {
  ReturnType: GasPrices;
  Parameters: [];
};

4. Send UserOperation using kernelClient

You should encode your initial transaction to include an approval of the required amount of ERC20 tokens for the paymaster client.

console.log("Preparing calldata");
const callData = await account.encodeCalls([
      // Approving the paymaster to use ERC-20 tokens for gas
      await getERC20PaymasterApproveCall(paymasterClient, {
        gasToken: gasTokenAddresses[sepolia.id]["USDC"],
        approveAmount: parseEther("1"),
        entryPoint,
      }),
      {
        to: zeroAddress, // Dummy call (replace with actual transaction details)
        value: BigInt(0),
        data: "0x",
      },
]),

console.log("Sending user operation...");
const userOpHash = await kernelClient.sendUserOperation({ callData });
console.log("UserOp taskId:", userOpHash);

5. Check UserOp status using Relay API

The userOpHash, when using the Gelato Bundler, is equivalent to the Task ID. This Task ID can be easily debugged through the Relay API, providing a streamlined method for troubleshooting and monitoring the status of transactions. Checkout here.

Explore the complete example code that demonstrates how to sponsor UserOps using Zerodev Paymaster with the ZeroDev Kernel here, as well as how to integrate with a Safe account here.