How to transfer token to the smart-contract?

Question

I've created the following mocked token:

//SPDX-License-Identifier: MIT

pragma solidity 0.8.17;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract Dai is ERC20 {
    constructor(uint256 initialSupply) ERC20("Dai Stablecoin", "DAI") {
        require(initialSupply > 0, "Initial supply has to be greater than 0");
        _mint(msg.sender, initialSupply * 10**18);
    }
}

And want to use it in this CrowdfundingCampaign smart-contract:

//SPDX-License-Identifier: MIT

pragma solidity 0.8.17;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

contract CrowdfundingCampaign {
    using SafeERC20 for ERC20;

    // Custom ERC20 token used for pledging funds
    ERC20 public token;

    // Address of the contract owner (the campaign creator)
    address payable public owner;

    // Funding goal of the campaign
    uint256 public fundingGoal;

    // The total amount of funds pledged
    uint256 public totalFundsPledged;

    // Mapping of addresses to the amount of funds pledged by each user
    mapping(address => uint256) public fundsPledged;

    // Event for logging state changes
    event FundPledged(address indexed _from, uint256 _amount);
    event RefundClaimed(address indexed _to, uint256 _amount);

    constructor(ERC20 _token, uint256 _fundingGoal) {
        require(
            _token.totalSupply() > 0,
            "Token contract must have a positive total supply"
        );
        require(_fundingGoal > 0, "Funding goal must be a positive value");

        token = _token;
        owner = payable(msg.sender);
        fundingGoal = _fundingGoal;
    }

    // Pledges funds to the campaign
    function pledgeFunds(uint256 _amount) public payable {
        require(_amount > 0, "Pledge amount must be a positive value");
        require(
            token.transferFrom(msg.sender, address(this), _amount),
            "Token transfer failed"
        );

        fundsPledged[msg.sender] += _amount;
        totalFundsPledged += _amount;

        emit FundPledged(msg.sender, _amount);
    }

    // Claims a refund for pledged funds if the funding goal is not met
    function claimRefund() public {
        require(
            totalFundsPledged < fundingGoal,
            "Funding goal has been met, no refunds available"
        );
        require(fundsPledged[msg.sender] > 0, "You have not pledged any funds");

        uint256 refundAmount = fundsPledged[msg.sender];
        token.safeTransfer(msg.sender, refundAmount);

        fundsPledged[msg.sender] = 0;
        totalFundsPledged -= refundAmount;

        emit RefundClaimed(msg.sender, refundAmount);
    }

    // Withdraws any remaining funds and ends the campaign
    function endCampaign() public {
        require(
            msg.sender == owner,
            "Only the contract owner can end the campaign"
        );
        require(
            totalFundsPledged >= fundingGoal,
            "Funding goal has not been met"
        );

        // owner.transfer(address(this).balance);
        // owner.transferFrom(address(this), address(this), _amount)

        token.safeTransfer(owner, address(this).balance);

        // token.transferFrom(address(this), owner, address(this).balance);
    }
}

I'm testing this smart-contract in Remix, and everything seems to work, but when I do web3.eth.getBalance("contract-adress"), it always displays 0. endCampaign also doesn't work because balance aren't changing.

What I'm doing wrong?

Answer 1

Two things to consider:

Make sure to approve the amount that you want transferFrom.

    function pledgeFunds(uint256 _amount, address token) public payable {
        require(_amount > 0, "Pledge amount must be a positive value");
        require(token.allowance(mmsg.sender, address(this)) > _amount, 
        "You need to approve first");
        require(
            token.transferFrom(msg.sender, address(this), _amount),
            "Token transfer failed"
        );

        fundsPledged[msg.sender] += _amount;
        totalFundsPledged += _amount;

        emit FundPledged(msg.sender, _amount);
    }

Also here's an example in ethers about the diference between token balance and eth balance: