What I did was generate playlists for MP3s in folders, and they consisted of the ff. format:
Folder1
A.mp3
B.mp3
Folder2
C.mp3
D.mp3
Playlists
Folder1.m3u
Folder2.m3u
I copied the folders to the Music directory in the internal storage in one phone and to the Music directory in the SD card or external storage in another phone.
I installed Symfonium and right after selecting the Music directories, edit the settings to automatically import playlists. After that, both phones started syncing.
For the first phone, the m3u files showed up correctly in the playlists section, but not in the second phone.
Is it possible that the process works for internal storage but not for external ones?
Lastly, is it possible to start from scratch, i.e., is there a reset setting in the app, such that I can delete the database contents and resync everything in case I made lots of changes with the source data? What I’ve had to do for now was uninstall Symfonium, reinstall it, and configure it once more.