10-11-2016 06:07
10-11-2016 06:07
10-12-2016 06:30
10-12-2016 06:30
A warm welcome to the Community @itstiff. Sorry to hear you're seeing a “400 error” when attempting to set up your tracker. I recommend checking if your iOS Fitbit app is updated by following @MarreFitbit's instructions in the How do I update the Fitbit app for iOS? post. After checking this, follow the setup procedure one more time.
I hope this helps, let me know the outcome.