How to fix invalid BigNumber string error in Solidity?

Question

this is a simple contract. where I want to develop a function, optimizer, upon calling it will transfer an amount of eth to an address. but when I deploy it on the testnet, connect my Metamask and try to call the optimizer function with 0.5 eth in Remix, its gives me this error:

transact to AB.Optimizer errored: Error encoding arguments: Error: invalid BigNumber string (argument="value", value="0.5", code=INVALID_ARGUMENT)

where is fault in my code?

    pragma solidity ^0.8.7;
    
    // SPDX-License-Identifier: GPL-3.0
    
    
    contract ABc {
    
       address payable  b= payable(xxx);
    
        uint amount= 0.4 ether;
      
    
    
         function Optimizer( uint256 _amount )public  payable{
    
            
         _amount=msg.value;
            
           require(amount >=0.4 ether,"transfer amount to low");
    
          
    
          b.transfer(msg.value);
    
          
           
        }
        
    }

Answer 1

You can't pass floating point numbers as input to a function in solidity, if you want to pass 0.5 ether, you would need to do so in terms of WEI, which would be 500000000000000000.

You have a few things in your contract that I revised here:

contract AB {

  error CallFailed();
  error TransferAmountTooLow();

    uint amount= 0.1 ether;
    address payable b = payable(0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2);


     function Optimizer( )public  payable{ 
      if(msg.value < amount) {
        revert TransferAmountTooLow();
      }
      (bool sent,) = b.call{value: msg.value}("");
      if(!sent) {
        revert CallFailed();
      }    
    }
    
}

1. Instead of using _amount to try and pass ETH, I removed this variable entirely. When passing value to a function you don't do so using an input parameter.

2. I changed your require statement that uses a hard-coded string to a more gas efficient custom error.

3. I changed your transfer to a call for sending ETH in a more efficient way, as well as validating that the call went through with an additional custom error.