function sendTokensArray(
        address[] beneficiaries, 
        uint256[] amounts
    )
        external
        onlyOwner
    {
        require(beneficiaries.length == amounts.length, "array lengths have to be equal");
        require(beneficiaries.length > 0, "array lengths have to be greater than zero");

        for (uint256 i = 0; i < beneficiaries.length; i++) {
            _sendTokens(beneficiaries[i], amounts[i]);
        }
    }