I would try restarting your phone and then restarting your fitbit using this procedure:
- Plug the charging cable into the USB port on your computer or a UL-certified USB wall charger.
- Remove the pebble from the wristband and press it into the compartment on the charging cable. The pins on the charging cable must align with the corresponding pins on the back of the pebble to lock securely in place.

You’ll know the connection is secure when the pebble vibrates and you see the indicator lights blinking.
- Find the button on the charging cable below the tracker compartment.
- Press it three times within five seconds. The tracker vibrates each time you press the button. A few seconds after the third press, all the lights will flash simultaneously. This means the pebble has restarted. If you miss the light flash but notice the pebble has resumed charging, that too is confirmation that the restart was successful.
- Remove the pebble from the charging cable and insert it back into the wristband.
Give this a few tries as it doesn't always work. 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/