flash loan always revert with revert UniswapV2: K

[stefdelec]

I am writing a fairly simple smart contract in order to do a flash loan but my transaction always revert with the following error UniswapV2: K. I have read 10 000 times the doc explaining the error, but I still don't understand what can be wrong in my code.

    function uniswapV2Call(
        address _sender,
        uint _amount0,
        uint _amount1,
        bytes calldata _data
    ) external {
        address[] memory path = new address[](2);

        address sender = _sender;

        address token0 = IUniswapV2Pair(msg.sender).token0();
        address token1 = IUniswapV2Pair(msg.sender).token1();


        require(
            msg.sender == UniswapV2Library.pairFor(dex1FactoryAddress, token0, token1),
            'Unauthorized'
        );

        require(_amount0 == 0 || _amount1 == 0, 'one amout should be 0');
        require(_amount0 != 0 || _amount1 != 0, 'one amout should be positive');

        uint amoutStartingToken = _amount0 == 0 ? _amount1 : _amount0;
        path[0] = _amount0 == 0 ? token1 : token0;
        path[1] = _amount0 == 0 ? token0 : token1;

        IERC20 startingToken = IERC20(path[0]);
        IERC20 targetToken = IERC20(path[1]);

        startingToken.approve(address(sushiRouter), amoutStartingToken);

        uint amountRequired = UniswapV2Library.getAmountsIn(
            dex1FactoryAddress,
            amoutStartingToken,
            path
        )[0];


        sushiRouter
        .swapExactTokensForTokensSupportingFeeOnTransferTokens(
            amoutStartingToken,
            amountRequired,
            path,
            sender,
            deadline
        );

        assert(targetToken.transfer(msg.sender, amountRequired));
        uint remainingBalance= targetToken.balanceOf(sender);
        assert(targetToken.transfer(tx.origin,  remainingBalance));
    }

For testing purpose I add a 'sync' and 'skim' on both pair before and after flash loan.

I had try this code on ganche-cli and prod and still facing the same issue. Is it a problem with the 'amountRequired' that I am paying back? In the docs it is said that it should be calculated with 'getAmountsIn', that is what I am doing.

What is wrong with my code? I asked on the discord channel + stackoverflow, but it seems no one there knows how to make a flash loan on unsiwap.

[germankuber]

I have the same issue.

[Samboy76]

I too have the same issue but during flashloan swap. Did you manage to find a resolution?

[CryptoFist]

seems it cuz of the requireAmount isn't proper