You'll have to use those names to call the web service to do a catalog search for the identifier, via https GET to api.music.apple.com and e.g. /v1/catalog/\(countryCode)/search. There's an example of this in Apple's sample code called "Interacting with Apple Music Content"/Adding-Content-to-Apple-Music - https://developer.apple.com/sample-code/wwdc/2017/Interacting-with-Apple-Music-Content.zip and explained in the video at WWDC 2017 Introducing MusicKit - https://developer.apple.com/videos/play/wwdc2017/502/.

I get this same error on latest Mac Catalyst, and similarly, the same code works perfectly on iOS in my case as well. This is specific to MPMusicPlayerController.applicationQueuePlayer (if I use .systemMusicPlayer instead, it does work on Catalyst... but systemMusicPlayer is not the behavior I want). Anyone else experience this? Should we submit it as a bug to Apple?

Check out: https://github.com/ethanhuang13/CupertinoJWT It works great, might be helpful for you!

Here's something to try if none of the previous suggestions work (although use at your own risk!)... Locate your ....pbxproj file and make a copy, just in case anything messes up. Open the ....pbxproj for editing, search for productRefGroup and delete that line. Save the edit and re-open Xcode. Products directory shows back up! Summary: I'm not sure if productRefGroup is really necessary! Everything seems to build fine without it.