pay_amt=500
buy_amt_min=0
route[0]=WETH
expectedMarketFeeBPS=1
require(
            ERC20(route[0]).transferFrom(
                msg.sender,
                address(this),
                pay_amt.add(pay_amt.mul(expectedMarketFeeBPS).div(10000))
            ),
            "initial ERC20 transfer failed"
        );
for (uint256 i = 0; i < route.length - 1; i++)

// here since route.length - 1 is 1-1=0 so loop will not run as i=0 and 0<0 is false
require(route.length>1, "Invalid route param");
