WeChat is free to use and there is no cost to the user. However, there are always extra options to add that may cost a fee. However, for most of the people out there, they use WeChat for free because it is an app that used for fun. However, if the app is being used for business purposes, then more options might be needed in order to fulfill their purposes. Then money might be needed to pay out.
Overall, the app and most of the functions are free. These apps are free because the company can make money in other ways. They can advertise for other companies. Since they have so many users, over one hundred million of them, advertisers would want to use them.