As Soundiiz is only able to do a matching process with metadatas (track title, artist name...), we are not using paths of your audio files.
Also, double check that in your Plex or Emby library, all metadatas for a song are well filled (title, artists and album). Because if, for example, artist field value is "Unknown"; Soundiiz will not be able to do the matching. Metadatas in your Plex/Emby should have exact same values than in your source file or music service.
That's why you should use the XSPF or EXTM3U format when trying to import playlist file to Plex or Emby instead of simple M3U.