Make sure you have enabled the notifications in the preferences.
1. Go to Notifications in your Preferences menu and make sure the box is selected.
If you go to Android OS settings --> device --> Apps --> DigiCal --> make sure that you have ticked "show notifications". (If you have this disabled, while notifications and pop ups enabled in DigiCal you'll only get pop ups but no messages in your notification tray).
It might also help to install Google Calendar app as it may fix the notifications.
Can you check if you have turned on the notification settings in DigiCal?
1) Preferences / Settings menu
3) Enable notification
Can you also check on your phone your notification settings?
1) Go to Android OS Setting Menu
2) Sound & Notification
3) App Notification
5) make sure you haven't blocked DigiCal notification.
Sometimes it also helps to restart your phone or reinstall DigiCal