My Garmin Vivosmart4 now won’t sync and Bluetooth is on. It synced earlier today but now will not- errors out.

Hello runnergirl95.

Please start by making sure that your mobile app is up to date:

Installing, Updating and Uninstalling the Garmin Connect App

Then, you can remove the watch from the app:

How Do I Remove a Device From the Garmin Connect App?

Finally, pair the watch again:

Instructions to Pair a Garmin Fitness Device to a Smartphone