Welcome to the forums @Tinashort
Try setting it back up as a new device on an existing account. Once unpaired, it can sometimes be tricky to get it to set back up.
Also, you can restart the Fitbit, which seems to help with trouble syncing.
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Allow me to help you @Tinashort! Thanks for the troubleshoot you've done. Besides the great tips that @Odyssey13 mentioned you may want to check this post from @SunsetRunner and double check those things.
Hope this helps. Keep me posted.
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