What is the ruling on registering in a new social media platform that grants subscribers, three months before its launch, a portion of its lifetime profits in exchange for bringing in other subscribers, knowing that it does not require any payment or purchase?

It is permissible to subscribe to the website and attract subscribers to it in exchange for a percentage of its profits if what is displayed on it is permissible, considering that the contract between you is a ju'alah (reward-based) contract, and there is no harm in it being continuous without a specified duration. However, if what is displayed on the website is forbidden, then it is not permissible to subscribe to it or attract subscribers to it, because Allah Almighty says: "And do not cooperate in sin and aggression."