The main thing is you need to set up your phone in MusicBee (configure the sync settings) and at least preview a wired sync in MusicBee. Then unplug the phone and try syncing with the app. The phone and the computer with MusicBee have to be on the same private network.
You might also benefit from updating to the latest beta (see my sig).
Be aware if you have Android 10 there have been some issues. Steven is working on a fix but it's not officially released yet.