Why there’re no calendars or events visible in Calendar Op.2?

Calendar Op.2 uses standard iOS Calendar app as a calendar database. Please follow the steps below to figure out what’s wrong.

1. First, please launch the standard ‘Calendar’ app from the home screen and make sure your data exists in it.
2. Then, launch Calendar Op.2 and open the Settings View and go to “Select calendars to display”.
3. Turn on all calendars you need and make them visible.