I am getting constant error in transfering erc20 tokens from users acc to this smart contract

Question

I am getting this 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" } }

This is my code:

address private sender; 

address private thiscontract = address(this);

function approveSmartcontract(IERC20 _token, address _sender, uint tokens)internal returns(bool)  {
    return _token.approve(thiscontract,tokens);
}
function transferfunds(address tokenadd,uint _tokens) public{
    sender = msg.sender;
    IERC20 token = IERC20(tokenadd);
    if (approveSmartcontract(token,sender,_tokens) == true ){
        token.transferFrom(sender,thiscontract,_tokens);
    }
}

}

why am I getting this error can someone pls provide the right code below that would work? please

Answer 1

The same question. The same answer man. When you are calling approveSmartcontract Then the msg.sender is the contract itself. it means when this function calls the approve function in the IERC20 contract then the msg.sender is this contract's address which is caling the function. Now the approve function works in a way that the parameter you pass gets the allowance to spend tokens on behalf of the msg.snder. This way when you call approveSmartcontract then the msg.sender and the parameter both are same i.e. the contract's adddress. And the transferfunds function is trying to send tokens from your wallet address to the contract and again the msg.sender is the contract's address when the transferFrom function is called in the ERC20 contract. And because your contract address is not approved to spend tokens on behalf of the wallet address, you are getting this error. To perform this asked you have to directly call the ERC20 approve contract either form the etherscan or you can write a small script to talk with the contract.

Answer 2

You need to approve the allowance of the token before you transfer the token to your smart contract you should call token.approve(sender, _tokens);

This will set allowance of the of the tokens for the msg.sender.