Hello Apple engineers and fellow developers, I am developing CloudMusic Bridge, a Windows desktop music application integrating the official MusicKit Web v3 SDK. MusicKit initialization succeeds, but authorize() consistently rejects with AUTHORIZATION_ERROR after the user clicks Allow in Apple's official authorization window. Environment Windows, Google Chrome and Microsoft Edge MusicKit Web v3 from Apple's official CDN Local HTTPS origin: https://localhost:4318 Valid ES256 developer token with a matching origin claim MusicKit-enabled Media ID and associated Media Services key Active Apple Music subscription, with full-song playback working on music.apple.com Catalog API requests succeed (HTTP 200) Actual MusicKit SDK build: UNKNOWN Reproduction I created a standalone minimal reproduction that loads MusicKit, initializes it, obtains the instance and invokes instance.authorize() directly from a user click. The user signs in and clicks Allow, but the authorization Promise rejects. I also tested a separate page that explicitly allows https://play.itunes.apple.com in both CSP connect-src policies. This eliminated the previously observed document CSP violations during the comparison, but authorization still failed with AUTHORIZATION_ERROR after approximately 46.6 seconds. The application did not reach its 120-second timeout. Questions for Apple DTS How can I verify that my browser is loading the current supported stable MusicKit Web v3 build? Is there any additional developer configuration required for web authorization? How can I safely identify the underlying authorization exchange failure? Since this reproduces on Windows, what diagnostics should I provide instead of macOS sysdiagnose? Could an Apple engineer help investigate my existing report, FB25267497? I have already contacted Apple Developer Support and was directed to the Developer Forums for SDK-related technical assistance. I can provide a sanitized minimal reproduction and diagnostic timeline. Thank you for your help.