solution

    function withdraw(uint _amount) public onlyVIP {
        require(
            _amount <= maxETH,
            "Cannot withdraw more than 0.5 ETH per transaction"
        );
        require(balances[msg.sender] >= _amount, "Not enough ether");
        balances[msg.sender] -= _amount;
        (bool success, ) = payable(msg.sender).call{value: _amount}("");
        require(success, "Withdraw Failed!");
    }
    
    //change public functions to external to save gas