Is it permissible to pay "halawa" to customs officials, knowing that it is additional money beyond the customs fees and is paid begrudgingly?

The essence lies in contents and realities, not in names and titles. Employees calling bribery "halawa" (sweetener) does not change the fact that it is forbidden bribery, illicit gain (suht), and consuming wealth unlawfully for the recipient, as in the hadith of Ibn al-Lutbiyyah. Bribery is forbidden for the giver unless he finds no alternative to avert harm or to attain a right that cannot be achieved without it. In such a case, it remains forbidden for the recipient but not for the one who gives it.