Norton is NOT and never has been user friendly for people like me, with less than stellar computer skills. I am offered cracked-screen protection for my I-phone, but Apple ( I never use their apps) will not accept my password for e-mail account. Guess I don't qualify for this protection plan. (My son originally set everything up for me.)
Here is the Norton Support article about the Screen Protection offer.
Apple is not involved in this program, so not sure where you are trying to sign in. Are you just trying to get the Screen Protection app? if so, be sure you are entering your Apple ID password for the download.
If your son set things up, maybe he will be able to help you.