First, you can log out of your account and then log back in again, or even delete and then reinstall the app (if you use it instead of the website). This will synchronize the app and correct possible minor bugs. If your PRO subscription is indeed active on your account, then you should be able to activate or deactivate Add-ons by tapping them.
You can also restore your purchases using your phone settings.
If the problem persists, contact technical support, who will respond as quickly as possible at firstname.lastname@example.org.