apple plus - something went wrong message

I signed up for Apple Plus streaming last week. I can successfully sign in on all my set top boxes except one. It refuses, returning a "Something went wrong - try again later" message. Well "later" has stretched into a week...  I've tried resetting the box both thru the on screen settings menu and by manually unplugging it - no dice. Is the box defective??? Can you run remote diagnostics??? Is there a tech I can call???