I have fairly extensive experience developing backends for online games. Whether you need a simple API to store basic user data and scoreboards ... or you need a real-time engine to drive a MMORPG ... or a payment backend to handle in game purchases ... I can make it happen. Whether you expect 100 simultaneous users or 100 thousand your backend will be fast and responsive so that you and your users can focus on the gameplay rather than the technology that drives it.