Most of the time this is because someone has another phone from initial setup and both phones are added in the account and the wrong one (the older one) is selected for alerts. Especially if the phones have the same name.
What you should do is delete your phone(s) from the Tappecue mobile app, log off and back on to read the current phone. Any session should be restarted to pick up the correct phone.
Here's how to do it..
Go to the settings in the Tappecue app, iOS is a bottom tab, Android is the hamburger menu in the top left.
select Device Management->View Mobile Devices and Delete, iOS slide from right to left, Android hard press and delete.
Go back to the smoking session tab, and logout at the top right.
Go to your Settings on your phone and select notifications and then Tappecue and make sure you have notifications on.
Go back to the Tappecue app and login and it will add your Phone back to your account.
Make sure to end any sessions and start a new one.
Often time the alerts are set as a media sound and not a notification sound. So you may have to turn up the media.
Also, on iPhones make sure the slider for notifications is not turned off.