Welcome to Smogon! Take a moment to read the Introduction to Smogon for a run-down on everything Smogon, and make sure you take some time to read the global rules.
Same thing for me, I've been using this app for a long time now and all of a sudden I can't mega evolve anything, tried relogging, closing and opening app, and reinstalling it and still a no go. But this is still a great app