Just got myself a Charge HR and set up my account on Fitbit. I downloaded the app on my iPhone 6 (on iOS 9.3). However, as I attempt to Log In to set up the tracker on my phone via the app, it logs me out immediately. I have restarted the phone, uninstalled and reinstalled the Fitbit app, yet it still logs me out instantly after I input my email and password at Log in.
I also set up a new account, went through the steps and faced the same problem (ie, being logged out instantly).
This means I can't even access the dashboard on the phone at all, nothing, zilch, nada, since I keep getting logged out. So somebody..help! 
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It's great to see that you've visited the Fitbit Community @milly_me. Sorry to hear about the issues you experienced to log in to your Fitbit account. I would recommend following these instructions. If you keep experiencing the same problem please be so kind to get in touch with the Support Team. Let them know the workarounds you performed so they can further investigate the issue.
Thanks for stopping by, see you around. 
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