What is the ruling on subscribing to a paid website to obtain a VIP membership in exchange for discounts and cashback on purchases?

It is not permissible to pay money for membership or to upgrade it in order to receive discounts or gifts, because that falls under the forbidden categories of gharar (excessive uncertainty), gambling (qimar), and maysir (games of chance). Maysir is any transaction based on competition, where one party is either a gainer or a loser.