I have been struggling for months to look for a solution between my provider and Ring. They are both faced with an internet sync issue between the both lines I believe. The app caters only to one data plan. Throw in your second line with Data and it becomes a problem your phone shows an error connecting.
In order for me to see live when I am out or check live stream not on a wifi connection at home or a business, only using mobile internet, this is how I set it up in my Cellular options. By turning off one of the lines I can see live.
Hope this helps!