A. To fix authorization errors, first, ensure that you are logged into your Apple Music account. Open the Music app, go to your account settings, and verify your login status. If you are logged out, log back in.
B. If you are logged in and still facing issues, try revoking and reauthorizing the app. Go to Settings > Music, scroll down to 'Apps Using Your Account', find MUBR, and select 'Remove Access'. Then, reopen MUBR and log in again to reauthorize.