I was having the same problem and found a solution.
Once you click "Grab your offer now!" it opens the web page. In the web address box the NOW TV pass code is at the end of the address, copy it and go back to manage your passes and paste it there. It worked for me.
Thankyou for that. Worked perfectly. Just to explain further though, if when you click, “grab your offer”, it goes to the website and just circles, then you need to access the last bit of the address. Click inside the address bar to reveal it.
The last bit looks similar to NOWefghijkl123. This is your code.
Copy the code then buy a pass using the code.