Sonim XP3

I have set events in my calendar, and as far as I can figure out, have set to send a reminder/notification two days before and 5 minutes before. I only get a notification tone at the actual time of the event. What am I doing wrong??? There is nothing in the user guide that helps - it pretty much tells me what the calendar does, but not how to actually do it or fix it if it's not working correctly.