Pay gas in ERC-20 tokens

Pay for wallet deployments, transfers, or NFT mints in ERC-20 tokens.

For a FunWallet to pay gas in an ERC-20 token, 2 assets must be staked in a Token Paymaster contract:

The native gas token (ETH if on Ethereum, MATIC if on Polygon, etc). This token must be transferred to the Token Paymaster contract.
The ERC-20 token to pay gas in. This token can be staked in 2 ways:
- By transferring the token to the Token Paymaster contract.
- By giving token spend approval to the Token Paymaster contract.

Quick start

Configure environment

Configure the options.gasSponsor environment variable to contain both the address of the gas sponsor & the name of the ERC-20 token to pay gas in. To learn more about gas sponsors for paying gas in ERC-20 tokens, visit the token sponsor section.

await configureEnvironment({
  gasSponsor: {
    sponsorAddress: "0x07Ac5A221e5b3263ad0E04aBa6076B795A91aef9" // Our test sponsor address on Göerli
    token: "usdc"
  }
})

Fun offers a publicly-available token sponsor on the Göerli testnet for developer testing purposes. Once Fun has completed smart contract audits, a production-ready token paymaster will be available for use on all supported networks.

,erc20-gas.jsconst ethers = require("ethers")
const { FunWallet, configureEnvironment } = require("fun-wallet")
const { Eoa } =  require("fun-wallet/auth")
const { fundWallet } = require("fun-wallet/utils")
const fetch = require('node-fetch')

const API_KEY = "MYny3w7xJh6PRlRgkJ9604sHouY2MTke6lCPpSHq"
const PRIVATE_KEY = "0x98e9cfb323863bc4bfc094482703f3d4ac0cd407e3af2351c00dde1a6732756a"
const DEST_ADDR = "0xd8da6bf26964af9d7eed9e03e53415d37aa96045"

const main = async () => {
  // Configure environment
  await configureEnvironment({
      gasSponsor: {
          sponsorAddress: "0x07Ac5A221e5b3263ad0E04aBa6076B795A91aef9" // Our paymaster address
          token: "usdc"
      }
  })

  const provider = new ethers.providers.JsonRpcProvider("https://goerli.infura.io/v3/9aa3d95b3bc440fa88ea12eaa4456161")
  const eoa = new ethers.Wallet(PRIVATE_KEY, provider)
  const auth = new Eoa({ signer: eoa })
  const uniqueId = await auth.getUniqueId()

  const funWallet = new FunWallet( { uniqueId } )
  
  const receipt = await funWallet.transfer(auth, {
    to: DEST_ADDR,
    amount: 10,
    token: "USDC"
  })
}

main()

This code will fail without step 2.

Give paymaster approval to spend ERC-20s from your wallet

When a FunWallet executes a transaction paying for gas in ERC-20s, the paymaster contract first calculates the amount of gas the transaction will take, then checks an oracle price feed to get the exchange rate between the native gas token & the ERC-20 token intended to pay gas in. Finally, the paymaster contract transfers the necessary ERC-20s to from the FunWallet to itself. I order for the paymaster contract to be able to do this, the FunWallet must give token spend approval to the paymaster contract.

const { TokenSponsor } = require("fun-wallet/sponsors/TokenSponsor")

// Get token sponsor object
const tokenSponsor = new TokenSponsor()

// Approve paymaster address to access predefined set of wallet funds
await funWallet.approve(auth, {
  spender: tokenSponsor.getPaymasterAddress(),
  token: "usdc",
  amount: 10000
})

,erc20-gas.jsconst ethers = require("ethers")
const { TokenSponsor } = require("fun-wallet/sponsors/TokenSponsor")
const { FunWallet, configureEnvironment } = require("fun-wallet")
const { Eoa } =  require("fun-wallet/auth")
const fetch = require('node-fetch')

const API_KEY = "MYny3w7xJh6PRlRgkJ9604sHouY2MTke6lCPpSHq"
const PRIVATE_KEY = "0x98e9cfb323863bc4bfc094482703f3d4ac0cd407e3af2351c00dde1a6732756a"
const DEST_ADDR = "0xd8da6bf26964af9d7eed9e03e53415d37aa96045"

const main = async () => {
  await configureEnvironment({
      gasSponsor: {
          sponsorAddress: "0x07Ac5A221e5b3263ad0E04aBa6076B795A91aef9"
          token: "usdc"
      }
  })

  const provider = new ethers.providers.JsonRpcProvider("https://goerli.infura.io/v3/9aa3d95b3bc440fa88ea12eaa4456161")
  const eoa = new ethers.Wallet(PRIVATE_KEY, provider)
  const auth = new Eoa({ signer: eoa })
  const uniqueId = auth.getUniqueId()

  const funWallet = new FunWallet( { uniqueId } )

  // Get token sponsor object
  const tokenSponsor = new TokenSponsor()

  // Approve paymaster address to spend ERC-20s from funWallet
  await funWallet.approve(auth, {
    spender: tokenSponsor.getPaymasterAddress(),
    token: "usdc",
    amount: 10000
  })

  const receipt = await funWallet.transfer(auth, {
    to: DEST_ADDR,
    amount: 10,
    token: "USDC"
  })
}

main()

Pay gas in ERC-20 tokens

Quick start

Configure environment

Give paymaster approval to spend ERC-20s from your wallet

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