Welcome to the Forums @Noel5285
At the moment, the Galaxy J3 is not part of the supported devices list. This means that the app has not been fully optimized to work with that phone.
As long as it fulfills the minimum requirements, Android 4.4 and Bluetooth 4.0, there is a possibility that it can work but we cannot guarantee it. Some users of unsupported devices have mentioned that following these steps helps with the syncing so you can try them, maybe they will work.
If none of the above works, you could try to use a computer or another mobile device to try and sync your Fitbit to your account. Click here to get instructions on how to sync with other devices.
Let me know if you have any further questions.
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