Hi @Anonymous User
My understanding is that the download feature only works on IOS or Android mobile devices where you can use the NowTV App from the IOS or Android Apps Store.
PC's or Mac's are not covered, because i believe you use an internet browser with the NowTV player software.
I don't use a Mac or PC so i can't confirm the above, but i am confident to say this is the case.
Maybe it's covered in this help guide.
https://help.nowtv.com/article/download-shows-or-movies-to-watch-offline
Looks like its Apple or Android phone or tablets only according to this help guide below.
https://help.nowtv.com/article/having-problems-downloading-shows
