The Gmail notification not working issue on android is apparently preventing you from staying up to date. Every android users encounter this problem for a lot of reasons. But don't worry, we have done our research and get all the solutions that you can use to fix the Gmail notification not working issue - 

1. Enable label syncing
2. Check the system notification settings
3. Turn off battery save or data server
4. Disable DND mode or Airplane mode
5. Enable notification from Gmail
6. Whitelist Gmail from system optimization
7. Clear the Gmail app cache and data
8. Re-log into your Google account
9. Set up Network provided Time & Time Zone.

For more read - https://www.apsense.com/article/how-to-fix-gmail-notifications-not-working-on-iphone.html