I have a MacMini M2 machine running Sequoia 15.1 OS. On this machine, I am running a Virtual Machine, utilizing the Virtualization.Framework, with the same OS version, 15.1.
Logging into my account in the System Settings is successful. Next, I need to add my account in Xcode 16.1. While the initial login is successful, Xcode immediately displays the following error:
Decoding Error.
There was a failure decoding response: (HTTP 401, 60 bytes) The data couldn’t be read because it isn’t in the correct format.
As a result, I cannot see any account information, teams, etc.
A very similar bug has been reported at this issue - https://developer.apple.com/forums/thread/759877, but there has been no progress or updates there.
Is there any chance to fix this and get it working?
I have some good news and some bad news. I’m gonna start with the good news because, at least for some of you, it represents significant progress.
The good news is that the issue covered by this thread (r. 131573827) is now resolved. I’m now able to:
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Install a macOS 15 guest on a macOS 15 host.
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On the host, log in to System Settings with an Apple Account [1].
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On the guest, log in to System Settings with an Apple Account [2].
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On the guest, launch Xcode.
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In Xcode > Settings > Accounts, add the Apple Account [3] from step 3 and successfully authenticate. No more “Decoding Error” (-:
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Create a new Mac test project, select my team in Signing & Capabilities, and build and run that project.
Yay!
I tested this with macOS 15.2 (host and guest) and Xcode 16.2.
And now the bad news. The change that allows the guest to log in with an Apple Account (step 3 in the list above) required a change to the UDID format, and such UDIDs aren’t yet supported by the Developer website. That means that you won’t be able to use restricted entitlements [4] in projects that you want to run on the guest Mac.
We’ve been discussing this new issue on a separate thread, and I’ll update that when I have news.
Share and Enjoy
—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"
[1] This is my main Apple Account, with two-factor enabled, obviously.
[2] This is a test Apple Account. I created one with two-factor enabled for this test. I encounter some weirdness when testing with an old account that doesn’t have two-factor enabled, but I decided not to investigate that in depth because two-factor is obviously the way forward.
[3] Well, it still says Apple ID (-:
[4] That is, entitlements that must be authorised by a provisioning profile. See TN3125 Inside Code Signing: Provisioning Profiles for more on that.
