Netflix has download limit on the number of titles you can download and the number of devices you can watch downloaded videos with one account. Thus some original contents are not available to download either. Even with some Netflix original TV shows or movies, Netflix don't own all the rights. Sometimes you cannot see the download option next to a certain movie or TV show because Netflix only has right to stream the title and is unable to let you download it. Netflix download feature is only available for: Windows PC or tablet on Windows 10 Version 1607 (Anniversary Update) or above iPhone, iPad, iPod on iOS 9 or above Android phone or tablet on Android 4.4.2 or later.
It is most likely that Netflix download is not working on your device because of one of the following reasons: Why Can't I Download Movies or TV Shows on Netflix? How to Download Movies and TV Shows from Netflix on Mac (opens new window) How to Record Netflix Streaming Videos for Offline Watching (opens new window)