Generally, payment - koha - is not liable for tax if it's a gift.
Koha given for something in return is not a gift but you may need to pay GST on this type of koha.
It's the same for money, goods or vouchers - koha - given to someone who does work for you. It's not a gift, as you got something in return. You will need to deduct PAYE on koha given this way.
It's best look at each situation on a case-by-case basis.