I had the same problem with a versa. Here's how I solved it, but I don't know if it will work for you. Also, I use an android phone so if you're on iphone I don't know if the steps will be the same.
First, go into the fitbit app and remove the versa from it
second, remove the versa from bluetooth devices
(if you dont already have the app and/or the device is not listed the first two steps wont apply to you)
Reboot your phone and make sure bluetooth and wifi are turned on
Make sure the versa is turned on (if you can see the red X, it's on) and put it in the charger
Next either install the app or open it if it is already installed.
Go to add a device and select the versa model that you have
The app should detect it and then ask for the number displayed on the versa's screen.
The red x should disappear and present you with the bluetooth key that the app is asking for.
Continue the setup as prompted.
If the setup completes successfully you're all set and the red x should not return. If it doesn't it will.
A lot of people are having issues right now with the firmware update so good luck.
