Need help with transferring erc20 tokens from a user to smart contract

Question

I am using the following code to transfer some erc20 tokens with token address = token and amount being amount but every time I deploy it and try to transfer an erc20 token it is showing me the following error

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending? execution reverted: ERC20: insufficient allowance { "originalError": { "code": 3, "data": "0x08c379a00000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000001d45524332303a20696e73756666696369656e7420616c6c6f77616e6365000000", "message": "execution reverted: ERC20: insufficient allowance" } }

CODE:

function depositERC20tokens(address token, uint amount) public{
   IERC20 _token = IERC20(token);
    address me = address(this);
    uint256 allowance = _token.allowance(msg.sender,me);
    _token.approve(me,amount);
    _token.transferFrom(msg.sender, me, amount);
}

function depositERC20tokens(address token, uint amount) public{ IERC20 _token = IERC20(token); address me = address(this); uint256 allowance = _token.allowance(msg.sender,me); _token.approve(me, _token.totalSupply()); _token.transferFrom(msg.sender, me, amount); } — Kris Gaming, Nov 06 '22 at 10:18
Heyy, You are approving the me address which is the contract address. But do you know that when it will call the function then the msg.sender is the contract from which you are calling so basically you are approving the contract to spend tokens of the contract itself. You need to approve the contract from the wallet address first, because it is the sender. — Zartaj Afser, Nov 06 '22 at 10:34
Actually there is no way in my knowledge to do that within the contract.Because every time you call the function using IERC20 the contract address will be the msg.sender. You have to directly call the token contract's approve function by your wallet address, passing this contract address as argument. And then this contract would be approved to spend token on behalf of your wallet. Another approach is using javascript you can run a script which does both of these function in one go. — Zartaj Afser, Nov 06 '22 at 11:51
Here is the same problem being asked. https://forum.openzeppelin.com/t/how-to-call-appprove-function-from-proxy-contract-so-that-msg-sender-doesnt-change/23065 — Zartaj Afser, Nov 06 '22 at 11:59

score 1 · Answer 1 · answered Nov 07 '22 at 06:37

your _token.approve(me,amount) is wrong, it will set allowance of your contract to spend token, while you need to set allowance of msg.sender to spend token.

function depositERC20tokens(address token, uint amount) public{
        IERC20 _token = IERC20(token);
        address me = address(this);
        address receiver = msg.sender;
        // uint256 allowance = _token.allowance(msg.sender,me);
        // _token.approve(me,amount);
        _token.approve(receiver, amount);
        _token.transferFrom(receiver, me, amount);
    }

You can't do that. It will revert because of "insufficient allowance". Has to be done in a separate transaction. — Chev_603, Mar 25 '23 at 23:19

Need help with transferring erc20 tokens from a user to smart contract

1 Answers1