I got this problem when follow the instruction,

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here my two contract: 1) token sale contract:

pragma solidity ^0.5.0;

import "./DappToken.sol";

contract DappTokenSale {

    address payable admin;
    DappToken public tokenContract;
    uint256 public tokenPrice;
    uint256 public tokensSold;

    event Sell(address _buyer, uint256 _amount);

    constructor (DappToken _tokenContract, uint256 _tokenPrice) public {
        admin = msg.sender;
        tokenContract = _tokenContract;
        tokenPrice = _tokenPrice; 
    function multiply (uint x, uint y) internal pure returns (uint z) {
        require(y == 0 || (z = x * y) / y == x);

    function buyTokens (uint256 _numberOfTokens) public payable {

        require (msg.value == multiply(_numberOfTokens, tokenPrice));
        require (tokenContract.balanceOf(address(this)) >= _numberOfTokens);
        require (tokenContract.transfer(msg.sender, _numberOfTokens));

        tokensSold += _numberOfTokens;
        emit Sell(msg.sender, _numberOfTokens);
        function endSale () public {

            require (msg.sender == admin);
            require (tokenContract.transfer(admin, tokenContract.balanceOf(address(this))));


2) token contract:

pragma solidity ^0.5.0;

contract DappToken {
    string public name = "Dapp Token";
    string public symbol = "DToken";
    string public standard = "DToken v1.0";
    uint256 public totalSupply;

    event Transfer(
        address indexed _from,
        address indexed _to,
        uint256 _value

    event Approval(
        address indexed _owner,
        address indexed _spender,
        uint256 _value

    mapping(address => uint256) public balanceOf;
    mapping(address => mapping(address => uint256)) public allowance;

    constructor(uint256 _initialSupply) public {
        balanceOf[msg.sender] = _initialSupply;
        totalSupply = _initialSupply;

    function transfer (address _to, uint256 _value) public returns(bool success) {
        require(balanceOf[msg.sender] >= _value);
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;

        emit Transfer(msg.sender, _to, _value);
        return true;

    function approve(address _spender, uint256 _value) public returns(bool success) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;

    function transferFrom(address _from, address _to, uint256 _value) public returns(bool success) {

        require (_value <= balanceOf[_from]);
        require (_value <= allowance[_from][msg.sender]);

        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;

        allowance[_from][msg.sender] -= _value;

        emit Transfer( _from, _to, _value);
        return true;


how could i fix this ?

This is my migrate scripts:

const DappToken = artifacts.require("./DappToken.sol");
const DappTokenSale = artifacts.require('./DappTokenSale.sol');

module.exports = function(deployer) {
  deployer.deploy(DappToken, 1000000).then(function() {
    var tokenPrice = 1000000000000000;
    return deployer.deploy(DappTokenSale,DappToken.address, tokenPrice);

  • I think we'd need to see your migration script if this is occurring during truffle migrate. – Thomas Apr 22 at 17:15
  • I already add the script, take a look – johnho.91 Apr 22 at 18:05
  • That's the migration contract. There should be a Javascript file in your migrations directory used to deploy your contracts to the blockchain. – Thomas Apr 22 at 18:10
  • I edited it again, please check it – johnho.91 Apr 23 at 7:20
  • Okay, that looks good. Locally I'm able to successfully deploy your project to Ganache. For which ever network you are deploying to, does your default account have an ETH balance? – Thomas Apr 23 at 12:35

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