With Android 5.1 and above application notifications are given a priority setting.
If you find yourself not receiving any notifications or ringtones on TextMe Up please change your notification priorities on your device settings.
-Go to System settings.
-In the "device" section select "Sound and Notification"
-In "Sound and Notification" scroll down and select "Application Notifications"
-Find TextMe Up in the list of applications and select it
-Set TextMe Up as a priority
You should now receive all TextMe notifications from then on.