errors.sol

pragma solidity ^0.8.0;

contract Donation {
    // input your default donor address
    address public donor = 0x5B38Da6a701c568545dCfcB03FcB875f56beddC4;
    uint constant DONATION_FEE = 2 ether;

    modifier onlyDonor() {
    require(msg.sender == donor,"Only buyer can call this.");
    _;
    }

    function setNewDonor(address _donor, address _recipient) public payable onlyDonor {
        uint bal = address(this).balance;
        uint amount = msg.value;
        if (msg.value <  DONATION_FEE) revert("Not enough Ether provided.");
        // Perform the buy operation.
        donor = _donor;
        payable(_recipient).transfer(amount);

        assert(address(this).balance == bal - amount);
    } 

}