Please note that Google has made the decision to remove third-party apps and clocks from the Fitbit app gallery for users in the European Economic Area in June 2024. Users in other countries will not be impacted. (Source)
In addition the most current Fitbit devices, e.g., Sense 2, Versa 4 do not support third-party apps and clocks.

Cozie Fitbit is such a third-party app. Hence, we have decided to stop the support of Cozie Fitbit.
As an alternative, we recommend using Cozie Apple.