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Community Moderator Alumni are previous members of the Moderation Team, which ensures conversations are friendly, factual, and on-topic. Moderators are here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Awesome to see you here @Brooks73, welcome! Thanks for jumping in @SunsetRunner. 
As @SunsetRunner mention this specific model or the Sony Xperia family is not in the list of compatible devices with Fitbit. 
Same thing happened to me, I have a phone that is very recent so is not in the list either. I've been having syncing issues for a while so what I did is try to "Force quit" the Fitbit App. And I noticed that my tracker syncs every time I do that. It syncs for call and text notifications too. But you'll have to try, as for better practices it's best to sync with a different device or computer.
Give it a shot and let me know if that works! 
Best Answer
Community Moderator Alumni are previous members of the Moderation Team, which ensures conversations are friendly, factual, and on-topic. Moderators are here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Awesome to see you here @Brooks73, welcome! Thanks for jumping in @SunsetRunner.
As @SunsetRunner mention this specific model or the Sony Xperia family is not in the list of compatible devices with Fitbit.
Same thing happened to me, I have a phone that is very recent so is not in the list either. I've been having syncing issues for a while so what I did is try to "Force quit" the Fitbit App. And I noticed that my tracker syncs every time I do that. It syncs for call and text notifications too. But you'll have to try, as for better practices it's best to sync with a different device or computer.
Give it a shot and let me know if that works!
Best Answer
Community Moderator Alumni are previous members of the Moderation Team, which ensures conversations are friendly, factual, and on-topic. Moderators are here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Hope you're enjoying your day @Brooks73! Have you tried by long pressing the back button. After a long back button press, tap the circled (x) button at the top right corner of the app you want to close or swipe it away. I have an Android phone but I friend of mine uses a Windows phone with the 8.1 update and this worked for him.
Let me know if you need anything else! 
Best Answer