Push notifications for Glip are only sent at each 60-second break in a conversation.
When you’re offline (i.e., sign out of Glip or close Glip) or inactive for 30 minutes or more, you will receive a notification at each 60-second break in a conversation. This is to avoid receiving multiple notifications for every single message in an active conversation.
It's also possible that you forgot to allow notifications for Glip on your device, follow the steps below to resolve the issue
There are only two options. One is to delete the app, wait a full 24 hours, and then reinstall. Or you may:
1. Delete Glip from your device.
2. Switch the device off completely and Switch it back on.
3. Go to Settings > General > Date & Time and set the date ahead a day or more.
4. Switch the device off completely again and turn it back on.
5. Reinstall the app.
Go to Settings > Device > Sounds and notifications > App notifications and make sure that “Block notifications” is set to OFF.