Able to sign into tv.apple.com, but not into the Apple TV app on my Macbook
I am able to sign into appleid.apple.com, tv.apple.com, and into Apple ID on my Macbook, but not into the Apple TV app on my Macbook.
When I open the Apple TV app on my Macbook (by doing CMD + Space, then typing "Apple TV" and hitting ENTER), I get a prompt saying "Sign-In Required" and it tells me to enter my Apple ID and corresponding password. I do so, and hit ENTER and the only thing that happens is that the same prompt ("Sign-In Required") opens up again. This keeps happening over and over again. I am never actually logged into the Apple TV app.
I know my Apple ID and password are correct because I have used them to log into appleid.apple.com, tv.apple.com, and into Apple ID on my Macbook.
I also know my Apple ID and password are correct because if I intentionally enter an incorrect password I get a message saying so ("Your Apple ID or password is incorrect"). Yet when I enter the correct Apple ID and password, all that happens is that a new "Sign-In Required" prompt opens.
I don't know if it's relevant, but my Apple ID is an email with a custom domain name ending in ".dev". I would hope the Apple Engineers would have foreseen this case, but who knows...
Please help!
I haven't been able to claim my free membership of Apple TV due to this bug since I got my Macbook a few years ago. I try every once in a while and it's always the same. Finally decided to post here.