On 1st of November, 2018, Android apps must be updated to target Android version Oreo or newer. This is not optional and enforced by Google Play.
The new notification channels / categories gives users more control over notifications, as you will be able to customize notifications in every app, but it has far more limitations than before - as an app, you cannot decide to make sound or not per notification, only per notification category.
Users on Android Oreo or newer will notice that some settings in the app have moved to the system settings. In general they've all become system settings which is why many of the options in the DigiCal settings page are now simply shortcuts to the system settings page for DigiCal's notification settings. This allows for more customization, but it also means that now if something breaks it's unlikely going to be fixable from our end.
1) Please first make sure that the main show notifications setting for DigiCal in system settings > notifications > all apps > DigiCal, is turned ON. You can also reach this place by clicking the "Notification settings" button in DigiCal's preferences page.
To change the sound, vibration, importance (peeking), click on the "Reminders" category.
Tap an item on this page to change it. On Oreo, you can change the importance, sound, vibration, notification dot, visibility on lock screen and do not disturb settings. This may change in a future version of Android.