Hi Pancras,
I posted this in the main thread by accident believing I was replying to this thread of yours, my apologies!
I've been having issues with authorization after switching from v1 to v3, have tried some of the suggestions you provided in a reply to a post of mine. Have tried to reach out to Apple Support a few times, though I haven't received any support that has helped me to move forward.
I have tested my token at https://jwt.io and I'm getting a "Signature Verified", tried multiple browsers in private/incognito mode, now when I try to sign into my Apple Account to test my player I am receiving an error that stats "There is a Problem Connecting. There May be an Issue with Your Network." (which is not the case).
I have tried everything I can think of, I'm at a loss and would appreciate any help to get my project moving forward. This is what I am seeing in the browser developer console (using Firefox):
Authorization failed: AUTHORIZATION_ERROR: Unauthorized MKError https://js-cdn.music.apple.com/musickit/v3/musickit.js:13 authorize https://js-cdn.music.apple.com/musickit/v3/musickit.js:28 asyncGeneratorStep$w https://js-cdn.music.apple.com/musickit/v3/musickit.js:28 _next https://js-cdn.music.apple.com/musickit/v3/musickit.js:28 media.mydomain.com:398:19 <anonymous> https://media.mydomain.com/:398