I have a ERC20 token and I have created smart contract to buy and sell the token. I have also created frontend with next.js and ethers.js everything works perfectly. I have also created an API to buy my token. My API works when I use the signer with a predefined private address. But my requirement is that the signer changes based on the user. I want to know how to implement that.(My code below works for 1 user because I am using private key of my address directly) what I want : Use the same code for different users

My API for buy_token:

import {ethers} from 'ethers';
import { createTokenSwapInstance ,provider } from '../../../helpers/contractInstance/tokenSwapInstance';
//import { tokenSwapAddress} from '../../../config';

export default async function handler(req,res){
    if(req.method === 'POST'){
        //Check if data is present
        const tokenSwapAddress = '<token address>'
        const numberOfTokens = req.body.numberOfTokens;
        console.log("numberOfTokens", numberOfTokens)
        if(numberOfTokens === undefined ||numberOfTokens === ''|| numberOfTokens === 0){
            res.status(400).json({success: false, msg: 'Number of tokens is required.'});
        const feePercent = 3;
        const tokenPrice = 0.0168;
        //Calculating total fee amount to pay
        const numberOfTokensinNum = Number(numberOfTokens)
        const numberOftokensinWei = ethers.utils.parseEther(String(numberOfTokens))
        console.log('numberOftokensinWei', numberOftokensinWei)
        const totalfee = (numberOfTokensinNum * feePercent)/100;
        const totalAmount = (numberOfTokensinNum + totalfee) * tokenPrice
        const totalAmountinWei = ethers.utils.parseEther(String(totalAmount))
        console.log('TotalAmount', totalAmountinWei)
        //Buy tokens
           const tx = await createTokenSwapInstance.functions.buyTokens(numberOftokensinWei,{
            value: totalAmountinWei,
            gasLimit: 5000000
           await tx.wait();
           res.status(200).json({success: true, msg:'Transaction Successful.'})
            res.status(500).json({success: false, msg:'Transaction Failed. Please try again.'})
        res.status(400).json({success: false, msg: 'Bad request.'})

My createTokenSwapInstance:

import { ethers } from 'ethers';
//import Web3Modal from 'web3modal';
import path from 'path';
import fs from 'fs';
import { sign } from 'crypto';

export const infuraId = `<END POINT>`

export const provider = new ethers.providers.StaticJsonRpcProvider(infuraId)
const signer = new ethers.Wallet('<PRIVATE KEY>', provider)

const swapContractAddress = '<TOKEN SWAP ADDRESS>'
const tokenContractAddress ='<TOKEN ADDRESS>'

const tokenSwapContractAbi = () => {
    try {
      const dir = path.resolve(
      const file = fs.readFileSync(dir, 'utf8')
      const json = JSON.parse(file)
      const abi = json.abi
      return abi
    } catch (e) {
      console.log(`e`, e)

  export const createTokenSwapInstance = new ethers.Contract(

1 Answer 1


You need multiple signers:

const signer1 = new ethers.Wallet('<PRIVATE KEY>', provider)
const signer2 = new ethers.Wallet('<PRIVATE KEY>', provider)
const signer3 = new ethers.Wallet('<PRIVATE KEY>', provider)

You can then call any function using connect method with the signer of your choice.

await createTokenSwapInstance.connect(signer1).buyTokens(...)

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