Is it permissible to make a purchase using a friend's number in multi-level marketing to benefit from a price reduction, knowing that he will earn profit points through this purchase, and knowing that subscribing to this system is forbidden?

Not all multi-level marketing is forbidden, and the ruling on your friend's participation depends on the type of marketing: if it is permissible, then there is no harm for you in buying through him; but if it is forbidden, then it is not permissible for you to assist him in it or to buy from him, based on the Almighty's saying: "And do not cooperate in sin and aggression." The participant is advised to abandon what is forbidden and seek lawful earnings.