Why doesn't Xfinity Stream app work on my LG OLED TV?

I have 2 LG OLED TVs, 77" C2 and 48" C3.  I recently downloaded the Stream app on both TVs via the LG App Store.  The app installs and launches to the "Sign On" page but nothing else.  Actually, the white Sign On button isn't active and can't be clicked.

I have deleted and reinstalled but no success.  Is this an Xfinity Stream app issue or LG WebOS issue?  I can't find a conclusive answer to this.

Please help.