Relatives borrow money and don't pay it back. How can they return it?

If it is a close relative, you can remind me directly and kindly. For example, you can just say jokingly: Is the XX money you borrowed before a New Year's greeting for me? Wise relatives will certainly understand what you mean and pay back the money. There is no need to get used to it if it is the kind of person who deliberately cheats and repeatedly fails to pay it back. Speak it out in public at the end of the year when the family gets together, so that other relatives can see their faces clearly. It is estimated that all relatives will stand on your side and can't stand the pressure of public opinion. That relative will also pay back the money.