The wrong or no timetable may be active.
The selected timetable is shown in the white bar at the top.
Tap the small arrow next to the timetable name (if you do not see an arrow, please look for the timetable using the magnifying glass) and select your class either using "My timetable", or in the section "Timetables" using "Classes".
Should this not help, please try deleting and recreating your user profile in the app.
You will find detailed instructions here.
Tip
If there are no timetables available to you or no lessons are shown, your school probably has not given you the respective permissions in WebUntis.
If recreating your profile did not help, please contact your school's WebUntis administrator.
If there are no timetables available to you or no lessons are shown, your school probably has not given you the respective permissions in WebUntis.
If recreating your profile did not help, please contact your school's WebUntis administrator.