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I would try restarting your phone and then restarting your fitbit using this procedure:
Another thing to try is to forget the fitbit in your phone's bluetooth settings. If it still won't sync after that then there are some more ideas to try in this help file: https://help.fitbit.com/articles/en_US/Help_article/1866/
Note that the versa only has enough memory to hold up to a week of detailed data between syncs. After that it starts to hold the data at a daily summary level. So, when you get it syncing again some of the data may look odd.