Q: Unable to sign in using my Apple ID & pword. iPhone 6s+ iOS 9.3.3

I'm trying to sign in to the beta software program. I've archived an iTunes backup and gotten to the Apple ID sign in page. Entering my data brings me right back to the same windows, as if my ID/p'word are wrong. They're NOT wrong.
It has NOTHING TO DO WITH iTunes but Apple won't let me ask the question without the field filled. dumphux