What is the ruling on profiting from promoting advertisements online, where a sum is paid to a website to promote a product, and then this sum is returned with a fixed profit after a specified period? Is it permissible to receive a bonus for introducing new members, along with a tax deduction upon withdrawing funds? Does this constitute usury (riba)?

It is permissible to profit from advertising promotion if the following conditions are met: that the subscription is free, that the advertisements are for permissible things, and that there is no deception involved. If the subscription is for a fee, then it is gambling and forbidden, as Allah Almighty says: ﴿O YOU WHO HAVE BELIEVED, INDEED INTOXICANTS, GAMBLING, [SACRIFICING TO] STONE ALTARS, AND DIVINING ARROWS ARE DEFILEMENT FROM THE WORK OF SATAN, SO AVOID IT THAT YOU MAY BE SUCCESSFUL.﴾ (Al-Ma'idah/90). If the advertisements are for something forbidden, then it is assisting in sin, as Allah Almighty says: ﴿AND COOPERATE IN RIGHTEOUSNESS AND PIETY, BUT DO NOT COOPERATE IN SIN AND AGGRESSION.﴾ (Al-Ma'idah/2). As for promotion combined with investment, it is not a permissible investment, because it combines usury of surplus (riba al-fadl) and usury of delay (riba an-nasi'ah), and because it lacks the conditions for investment, which are: agreement on a percentage of the profit, not of the capital; no guarantee of the capital; and that the field be permissible.