Basic functionality of my iOS app now runs under Mac Catalyst. I can build and run on my local Mac, and create an archive for upload. When I first tried to validate this archive, the App Store automatically created a Mac certificate for me, and then created a package and signed it. So far so good.
Trying to validate or upload the app, however I get an App Store Connect Operation Error: No suitable application records were found. Verify your bundle identifier 'maccatalyst.com.mycompany.myapp' is correct.
In App Store Connect I cannot add a macOS version to my iOS app as would be logical, so I try to add a New macOS App, as suggested at WWDC 2019. modulo some terminology changes. There I get the error popup: You have no eligible Bundle IDs for macOS apps. Register one here.
Trying to register the bundle ID. I get the error message: An attribute in the provided entity has invalid value. An App ID with Identifier 'maccatalyst.com.mycompany.myapp' is not available. Please enter a different string.
What is a valid value for the bundle ID for a Mac Catalyst app to register in App Store Connect?
Yes, of course I use my real company name and real app name instead of the generics above. I use exactly the bundle name that Xcode created for me when I checked the Mac checkbox in Deployment Info in Xcode.