It turns out that ids are different across different catalog locales, but there is an easy way in the API to find equivalent items. That's actually the first topic covered in this WWDC session from last year: https://developer.apple.com/wwdc21/10293. If I were you, I'd be cautious about caching that id information, or at least making sure you gracefully handle the case where an item is no longer accessible at the id you have saved for it. I've seen a handful of cases in my own app where an album's id changes for whatever reason.

I haven't played around at all with the curator stuff -- @JoeKun, that post is a great overview and has me playing around in Postman. One thing I haven't been able to figure out: is there any particular rhyme or reason to the order in which the API returns the Playlist relationships? Taking your example of Apple Music Pop, I had expected the API to return the playlists in an order roughly equivalent to the page in Music.app. The most popular playlists first, which as I look now at Music.app on my Mac are "Today's Hits" and "Viral Hits." These are the two playlists returned from this endpoint, which I don't see anywhere on the Music.app Apple Music Pop page: "name": "Tom Mann: Songbook", "url": "https://music.apple.com/us/playlist/tom-mann-songbook/pl.b5a5fecc589d4056be182e8cafdc0fc0" and "url": "https://music.apple.com/us/playlist/ivan-dorn-essentials/pl.362b70aa54e54989a08a2e2df4ff48d3", "name": "Ivan Dorn Essentials", The Albums relationship for Artist seems to be more or less by popularity, but that doesn't seem to be the case here. Any hints at how to best make use of that resource?

I filed feedback FB9851840 (including sample project) reporting this very issue just moments before seeing this post. I get the same error as you. The documentation page for MusicPlayer does not mention it is available in macOS, but says it is in Mac Catalyst 15.0+, so it's not clear what is supposed to work. Perhaps @JoeKun can shed some light on the expected behavior of this API? I am really hoping to bring my iOS music player to the Mac in the future.

FB9558364

I am seeing very similar behavior on iOS 15 in my app. Installing it fresh on iOS 14 allows it to upload the initial data and start syncing, but doing the same on the latest iOS 15 beta causes the app to crash while in the background using 100% CPU, and it never manages to upload any data. I've submitted this as FB9489988, which also references an issue I've seen on both iOS 14 and iOS 15 around cpu_usage_fatal crashes when syncing with iCloud.

I still have not figured out what is causing this. Am I really the only person getting cpu_usage_fatal crashes caused by CoreData/CloudKit syncs?