We are using the official Apple Music API to get your Apple Music datas and also moving your playlists and favorites to this platform.
Unfortunately, Apple has removed "Delete" methods from his API, that means we are no more able to delete tracks in a playlist or delete a playlist.
That's why you got an error 104 "Feature not available for this platform" if you are syncing with a "Replace" method or using any "Replace to" feature for example.
Workaround when using "Synchronization" feature
While it's impossible to sync properly with an Apple Music playlist as destination (also, because the Apple Music API doesn't playlist in your curator profile); it's could be a great solution to use Apple Music as source of your Syncs !
For that, it's pretty easy. Go to the Apple Music playlist and use Share option, copy link and get the URL. Once done, you can simply create a new Sync and in source, use the first option "Playlist URL" and pasting here the previous URL.
Now, Soundiiz will use this Apple Music playlist as source for your synchronization to other music services and DSP !