Hi @Dan14502 and welcome to the forums. Please try the procedures I listed below. Hopefully, that will snap everything back to normal.
- Sync your device then if you can ... then in the app, select Account (at the top, left), name of your device, then scroll down to remove this device.
- Remove the Fitbit app from your phone.
- Restart your Fitbit device.
- Power the iPhone off. Wait a few minutes then power it back up.
- Reinstall your Fitbit app. Log in to your account if prompted.
- In the app, tap Account then Set Up a Device.
Let us know if this resolves the problem.