function buyTokens(address _beneficiary) public payable {
        require(!blacklisted[msg.sender], "Sender is blacklisted");
        bool preallocated = false;
        uint256 preallocatedTokens = 0;

        _buyTokens(
            _beneficiary,
            msg.sender,
            msg.value,
            preallocated,
            preallocatedTokens
        );
    }