Phantom notifications are similar to notifications that alert you of a new message or an existing message that has not been read.
To resolve this issue, please follow these steps
Restart your session on the app. Log out and log in again.
Clear your mobile app cache:
When on the app, click on the More tab in the bottom right corner.
Click Edit your profile below your photo, name, company, and title.
Click on the bar marked Edit account information.
Click “...” in the top right corner and select Clear app cache.
Delete the app and reinstall it.
3. If the issue persists, please try to reset it on the app from your phone settings.
Your phone Settings
Navigate to Notifications
Select Brella
Then, enable the Notifications button and turn off the Badge button.
Then, check Brella, you shouldn't see any notifications anymore.
Turn it on back again so you keep receiving notifications from Brella for future events.
Refer to the article here for more information on clearing app cache on your mobile