On my iPad Pro (iOS 10.2.1) running the latest version of Safari, the orange “Plus” button does not show up in the bottom right corner. I also tested on Chrome for iOS and Dolphin browser on iOS as well.
I finally went to my Mac and logged in there and the button showed up.
However, I did see the Add panel button under the “My Panels” tab on iOS.
Customer support service by UserEcho