Greetings, catherinefromhudson.
I see that you're having problems downloading songs using iTunes on your MacBook Pro. You're receiving an error 8104, and it's saying there was an issue with some purchased items. I'm happy to help.
Get help with iCloud Music Library
First, check iTunes to see if the song is ineligible for upload. Additionally, if you added the song to your library from the Apple Music catalog, it might no longer be available on Apple Music.
Check your Internet connection
Open Safari on your iOS device or Mac, or a web browser on your PC, and go to any website to make sure that you have a strong Wi-Fi or Internet connection.
If you can't connect to a Wi-Fi network on your iOS device, you can try using cellular data:
- Go to Settings > [your name] > iTunes & App Store.
- Turn on Use Cellular Data.
You might have to pay a fee to download over a cellular network. Contact your wireless carrier for details, and learn about cellular data settings and usage.
Use safe mode to isolate issues with your Mac -- If the previous steps didn't resolve the issue, restart your Mac in safe mode and test how it responds. Afterwards, reboot normally and log into your own user account. Remember this when booting in safe mode: Graphics performance limited in macOS Recovery, safe mode, or Guest User mode
How to test an issue in another user account on your Mac -- If the issue is also happening in safe mode, use this article to create and test a new user account. This will demonstrate if the issue is isolated to your account, or if its system wide. You'll need to sign into iTunes on this new user account in order to test the issue.
Let me know how that goes, and take care!