ERC20 Approve call to use tokens in another smart contract

Question

I am trying to build a smart contract that is using my custom token. Below you can find the sample of smart contract that I have created that showcases the approve function.

// SPDX-License-Identifier: GPL-3.0-only
pragma solidity ^0.8.11;

import "IERC20.sol";

contract Contract {

address public contractOwner;
IERC20 token;

constructor() {
    token = IERC20(0x000000000000); //your token here
    contractOwner = msg.sender;
}

function Approvetokens(uint256 _tokenamount) public returns(bool){
   token.approve(address(this), _tokenamount);
   return true;
}

}

Then, in my react application I am using a function to call the contract like so:

async addTokens() {
let abc = process.env.myPrice // where I have tried with either 1 or 1*1000000000 (as my token has 9 digits)
await this.state.myContract.methods.Approvetokens(abc).send({
  from:this.state.account
});
}

The contract gets called and metamask is opening the transaction, but the price to pay is HUGE, please see the screenshot below. I am connected to the fantom test network, but replicated this in Rinkeby as well.

I do not understand what I am doing wrong here...

Answer 1

The issue here is that the code you had mentioned is trying to approve from the contract's address.

token.approve(address(this), _tokenamount);

Approve function in ERC approves Approvetokens functions, it'll call the approve function in the ERC20 contract. For that call, msg.sender will be your contarct, not you. Since the contract doesn't have sufficient balance, it'll fail with Insufficient balance.

To approve your contract to spend your tokens, you'll need to call the token's approve function from your address. Hope this clarifies your question.