Family Sharing when Apple ID is not an @icloud.com

I want to Family share my Apple TV+ with my adult sister.

However she does not own any Apple products. She's on Android (yuck), anyway. She created a new Apple ID but used her gmail.com email address.

When she tries to access Apple TV+ it tells her she needs an "iTunes account. Enter code". What does this mean and what code is it talking about?

I tried similar and created a new AppleID using my gmail address and got to same error. What Code is it requiring as I tried the TV+ app code (from my PS4), and it just came back to a login screen.

Any help?