This error occurs when you have not given the app permission to access the Fitbit fields (or it has expired).
Try logging out of Fitbit in our app (Settings -> Log Out). Then close the app, reopen, and log in. You should see a permissions page like this:
Make sure to allow all permissions. Profile is required as well as any fields you plan to sync.
If logging out and logging back in does not show you this screen, you can also go to the Fitbit website:
- Go to fitbit.com and click My Dashboard
- Go to Settings
- Go to Applications
- Click "Revoke Access" on myFitnessSync
- Now log in to Fitbit again through the app, and you will get the permissions screen