I was trying to use the realtime board to create some wireframes for desktop website and later create a rapid prototype using another tool. I saw a functionality within realtime to create a frame and within that frame one could get a specification for desktop, mobile etc. When I did that and uploaded it in the prototyping application, the wireframing ended up getting zoomed by default to more than 1000%, not sure if you have used the tool for wireframing but that typically is a problem in wireframing phase and I wanted to see if you had created wireframes with intent to rapid prototype using realtime board.
Here is the 1 screen prototype link: https://projects.invisionapp.com/share/86N6BVLZEVK#/screens
I exported the frame using the process your help material has and selected that individual frame: