After an update, some users may experience the app not restoring previous purchases. 

Please follow these steps:

  1. Uninstall the app
  2. Turn your phone off and wait 30 seconds.
  3. Reinstall the app
  4. Restore your purchases

That should get you back up and running.

If you are still having issues it may be because certain phones do not flush the memory properly and may need to have the cache cleared. The following should fix those rare cases:

The app cache (and how to clear it)
  1. Open the Settings of your phone.
  2. Tap the Storage heading to open its settings page. ...
  3. Tap the Other Apps heading to see a list of your installed apps.
  4. Find the application you want to clear the cache of and tap its listing.
  5. Tap the Clear cache button.
  6. Restart phone, wait 30 seconds
  7. Reinstall the app
  8. Restore your purchases