The main reasons for not seeing notifications on Facebook include disabled notification settings (both in the phone settings and Facebook app settings), Do Not Disturb (DND) or Airplane mode being turned on, muted people or pages, using an outdated Facebook app version, and unstable internet connection. Common fixes are:

• Check and enable notifications in both phone settings and Facebook app settings.
• Make sure Do Not Disturb mode, Airplane mode, and Low Battery mode are off.
• Unmute friends or pages on Facebook to receive their notifications.
• Update the Facebook app to the latest version.
• Ensure a stable internet connection.
• Clear the app cache and data if glitches persist.
• Restart your phone to fix temporary issues.

These steps usually resolve the problem of Facebook notifications not showing up.