Build me a cross Platform(iOS/Android) Application

Want to get an app on Flutter or any suitable platform such that it supports both iOS and Android. The App will be created such Users can post queries and other users can answer them, similar to Quora/Reddit. But there will be special threads for each question based on the category and the user can tag other people specifically, or post their queries in those user's forums to answer that question. Also want to add credit system such that these credits are took from the user asking question to the user who was tagged to answer specifically when they answer the question successfully.

Will explain the project in more detail on chat during project posting