When users are not receiving reminders or notifications, there could be either 1 or 2 things happening.
Permissions are not set in the app setting or notifications are not allowed in your smart phone settings.
1. Go to Menu - Settings - App Permissions - Notifications. Set notifications phone setting to 'Allow Notifications'.
2. If you also have any user set reminders, you can review these settings by going to Menu - Reminders.