Does this solution work now across the board or am I just lucky??
SUCCESS I used my gmail E-mail instead of Username and it verified, took 3-5 minutes but did it.
I just signed up for the 3 week free trial.
I tried adding source with my actual Username and got the failure.
Tried with my email and it worked !!!
I am on latest stable release Version 2023.08.07.2138
I did not set up Family Sharing or 2FA.
EDIT: BTW when using the YTTV app there are 4 pre-selected Multi-screens which work in the YTTV app.