Is it permissible to marry online a Muslim or non-Muslim woman, with an agreement to waive the Mahr (dowry) and maintenance in case of divorce, with the woman's consent?

It is not permissible for a husband to stipulate to his wife that she must return the Mahr (dowry) or maintenance upon divorce, for that is a grave sin and manifest falsehood, based on the words of the Almighty: (And if you wish to replace one wife with another and you have given one of them a Qintar [a large amount of gold], do not take anything from it. Would you take it in falsehood and manifest sin?) and His words, the Almighty: (And it is not lawful for you to take anything from what you have given them).

However, if the divorce is at the wife's request for no fault of the husband, then the husband may refuse to divorce her until she ransoms herself from him by returning all or part of the Mahr, based on the words of the Almighty: (And it is not lawful for you to take anything from what you have given them, unless both fear that they will not be able to uphold the limits of Allah). As for maintenance, it is not permissible to withhold it from its rightful recipient or to reclaim it after it has been given.

Therefore, the aforementioned condition is void, and the woman is not obligated to fulfill it.