I have been able to cast from my iPhone to NOW TV box, but also have a Smart Stick elsewhere in the house and for some reason the iPhone app isn’t showing that as a device I can cast to. Any ideas?
Bit of a long shot, have you tried a fresh NowTV App download from your iPhone Apps Store, then sign back into the newly downloaded App with the same account details used on your NowTV Box & Stick.
Also make sure your iPhone is on the same WiFi network has your Box & Stick.
i am not familiar with iOS, but it might be worth reading this link article as well about version 9 &10 will not be supported soon.