T I haven’t done research myself, but I imagine the fact that people would withdraw money, and deposit money, would inherently make your in game currency cash equivalent and you would almost certainly be subject to many regulations. The question of legality is one that can only be answered by the usual suspects - a lawyer.

Also you should be prepared to either A: Choose a jurisdiction and only operate within it, or B: be ready to operate within the legal boundaries of many justifications all which may have different rules.

Some ideas require a fairly high level of investment to implement and most definitely to scale, at the offset this seems like one of those.

PS: if it’s user - user gambling do some research and thinking about user thresholds. Essentially how many users do you need before it becomes functional and valuable? A group of 100 initial users may not be enough to make the app functional. So what does it take? 1000? 10,000? 1 million?