I just installed the pro version. Why does the app still prompt me to purchase it when I try using pro features?

Because the free and pro versions are two separate apps, they each require their own shortcut on your home screen.  Most likely you have launched the free version by using your old shortcut.  Please uninstall the free version (recommended) and create a new shortcut for the pro version on your home screen.n nNewer versions of the free and pro apps warn you if the other version is also installed on your device.