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I'm using Remix with a Foundry Provider.

I'm trying to create a smart contract to swap between 2 or several tokens. I have no issue when I compile and deploy the contract, but when I call the swap function, I have this message :

Gas estimation errored with the following message (see below). The transaction execution will likely fail. Do you want to force sending? execution reverted

And when I send the transaction execution, I have this status :

false Transaction mined but execution failed

Do you any ideas why ? I tried to increase the gas limit, but it's not working.

This is my code :

pragma solidity >=0.8.7;

interface IERC20 {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external view returns (string memory);
    function symbol() external view returns (string memory);
    function decimals() external view returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);
    function deposit() external payable;
}

interface IQuickSwapRouter
{
    function swapExactTokensForTokens(
        uint amountIn,
        uint amountOutMin,
        address[] calldata path,
        address to,
        uint deadline
        ) external returns (uint[] memory amounts);
}

contract swapToken {

    function swap(address contractRouter, address tokenAddr, address[] memory path, uint256 nbtoken, address to) public {
        

        IERC20(tokenAddr).transferFrom(msg.sender, address(this), nbtoken);

        IERC20(tokenAddr).approve(contractRouter, nbtoken);

        IQuickSwapRouter(contractRouter).swapExactTokensForTokens(
        nbtoken, 
        0, 
        path, 
        to, 
        block.timestamp);

    }
}
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  • There are a lot of possible reasons. Doesn't remix show you a revert reason/string?
    – 0xSanson
    Aug 13 at 17:59
  • No, except those two messages, I have nothing else.
    – dinamo
    Aug 14 at 8:18
  • Can you share a failed transaction hash? Do the tokens have a fee on transfer?
    – Ismael
    Aug 14 at 15:36

1 Answer 1

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I find the solution by commenting the line : IERC20(tokenAddr).transferFrom(msg.sender, address(this), nbtoken);.

It's working well:)

1
  • Are you sure that it will work? By removing that line you are requiring the contract has enough of the input tokens.
    – Ismael
    Aug 16 at 1:33

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