This is a J series model from 2015.
Where according to this NOW article in the link below NOW only supports Samsung 2016 models onwards.
I am assuming there is no NOW App showing in the TV Apps Store ?
You will need something suitable from this list in the link below.
NOW don't sell their NOW streaming boxes or Sticks anymore, where they have been discontinued for a couple of years now.
If you don't own a suitable device from the list, then look at something like a Roku or Amazon Fire Stick.