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). If that doesn't work, try restoring your purchases on iOS. 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.
Other FizzUp PRO feature: the Focus programs are available right in the application. Tap the "star" icon in the tab bar to access them.
If they're still not activated, contact technical support, who will respond as quickly as possible at email@example.com.