In order to receive notifications on Android, you must have the Google Play Services App installed and updated. This is vital because our notifications are sent through Google. Please make sure the Google Play Services App is installed and updated to the latest version.
The Google Play Services App can be found here: https://play.google.com/store/apps/details?id=com.google.android.gms
If this fails to resolve the issue or you have this problem with your iPhone, please send us feedback (Main Menu > Settings > Send us Feedback.