I have been a fully paid up member with NOW TV sport. I have a Smart TV. When I go into sport it takes me to talktalktv sport and requests me to sign up. I am already signed up. I do not have a Smart phone so cannot scan anything.
If you are already in the NOW App from the UK and it is asking for a QR Scan code, then keep pressing the OK / enter button on your remote and when you see the main NOW home screen page, navigate down to the bottom of the screen.
Where on the bottom grid row there should be My Account, click on My Account and login with your NOW account details.