Can you get an activation code for a Fire TV Stick from a mobile phone? Maybe I'm officially a caveman, but I don't think it works that way.
I have been subscribing to HBO through Cox for almost 10 years. When I first subscribed, HBO On-demand through Cox had very sparse programming. I think on-demand would rotate only 10-12 movies each month. It was awful, so I bought a Roku to access more content via the Internet.
When I first activated Roku, HBO Go assigned my Roku an activation code. I had to then use a browser, create an account on hbogo.com and enter the code with all my details. I think I also had to create an account on roku.com, but I think it was to activate my Roku. I can't remember.
I think activation codes are device specific. Maybe times have changed.