How do I unlock the upgrades that are just question marks? I have the paid version and I'm not sure if I'm doing anything wrong, or if they're just their to taunt me.
They are probably broken/unfinished, and that's why they're still locked. Recently we made a choice to add upgrades to every stage (before they were scattered) so some of them are new and definitely not "real" yet. But they will be! We are taking a short break to address feedback and fix stuff, and then we'll be back to making that stuff work. :) You're definitely not doing anything wrong!