uniswap solidity contract: swapExactTokensForTokens Failed

Question

I used transferFrom and approve, but still got this error:

execution reverted: UniswapV2Library: INSUFFICIENT_INPUT_AMOUNT.

I read the source code of Uniswap, in_ may be 0 ?

This problem has been solved, and now there are new error, execution reverted,There should be an error during the swap

This is my complete code

  function swap3(uint256 amountIn,uint256 amountOutMin,IRouter _router, IERC20[] calldata path, uint256 deadline
    ) external payable returns (bool b)  {
            require(address(path[0]) != address(0) , "path[0] error________");
            require(address(path[1]) != address(0),"path[1] error________");
            require(address(_router) != address(0) ,"_router error________");
            require(amountIn > 0 ,"amountIn must be > 0");
            IERC20 er = IERC20(path[0]);
            address[] memory n_path = new address[](2);
            n_path[0] = address(path[0]);
            n_path[1] = address(path[1]);
            require(er.transferFrom(msg.sender, address(this), amountIn),"transferFrom failed______");
            require(er.approve(address(_irouter), amountIn),"approve failed_______");
            require(er.balanceOf(address(this)) > 0 ," contract no money_______");
            IRouter(_router).swapExactTokensForTokens(amountIn,amountOutMin,n_path,msg.sender,deadline);
            return true;
    }

I don't know how to solve it now

Answer 1

The error (link to code) happens when the starting amount (in_) or an intermediate amount is 0.

So you need to use in_ > 0 and make sure that n_path has enough liquidity to output amounts > 0.