Can't Purchase Power Pack?
If you can't purchase the Power Pack, try this:
1) Turn off purchase restrictions in your phone settings. You can do this in settings > general > restrictions. Make sure in-app purchases is enabled. More info here: https://support.apple.com/en-us/HT204396
2) If it still doesn't work, you may be using a different Apple ID account than when you download the app. Apple requires you to use the same. The easy fix here is to uninstall the app and install it again. Make sure you login with google/facebook in our app first so your workouts are backed up. Then just uninstall/reinstall the app and try to purchase again.