iTunes keeps asking for password on MacBook

On my brand new Macbook - running MacOS 10.13.6 - iTunes is popping up with a window that asks me to "Sign in to the iTunes Store" over and over again.

If I press cancel it pops straight back up, if I enter the right password it pops straight back up, the only way to stop it is to force quit iTunes. I know that the password I am entering is correct because when I enter the wrong password, i get the red messaging that my password is incorrect.

All iTunes menus are unavailable to me when I can't log in.

I've seen similar issues on this forum but all solutions rely on being able to use iTunes drop down menus, they are all greyed out for me no matter what password I use. Completely unworkable, please help.