Welcome to Android Central! I have a Fitbit as well, though not the same model as yours. If you press and hold the button on the side of your Fitbit, do you see options about activating the Fitbit when you move your wrist; Notifications; etc? If you see the Notifications option, tap it. You will see a phone with a message icon on it. If it is crossed out, tap it to turn it on. Then, you should be able to receive text message notifications on your Fitbit.
Keep us posted on what happens!
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