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Hello @Walter503, thanks for joining the Fitbit Community, it's great to have you on board. 
I appreciate your participation in the Forums and for reporting this situation to us. First of all, if you haven't done it yet, please restart your Flex 2. If your tracker is still unable to receive Notifications, please try the following steps:
- Go to the Bluetooth settings on your phone and tap on tracker. Then tap on Forget this Device.
- Force-close the Fitbit app by double tapping the home button on your phone and swiping up the app.
- Open the app again and tap on Account > Your Tracker > Notifications. You will receive the following Pop-up:
- Then, once you tap on Set Up, the app will begin setting up your tracker with the Bluetooth on your phone, which will prompt the next pop-up:
- Tap Pair
- Once you get back to the tracker options, tap on Notifications an enable the ones you'd like to receive.
Additionally, please go to your phone Settings > Notifications > Fitbit and Settings > Notifications > Messages and check that the following is enabled:
- Allow Notifications
- Show on Lock Screen
- Show in History
I hope this can be helpful, give it a try and keep me posted in case you need anything else.
Best Answer