What is the ruling on earning money through affiliate marketing for the Khamsat website, knowing that the site pays $2 for every new user who registers through the marketer and purchases at least one service?

Brokerage, where the website takes a portion of the price of a sold good or provided service, is permissible, provided that the commodity or service is Islamically permissible. Likewise, attracting customers to the website in exchange for a known commission is also permissible and is considered a legitimate ju'ala (stipulated reward), provided that the agreed-upon work is Islamically permissible. So, whoever completes the work after knowing about the ju'l (reward) is entitled to it.