OK....here's my first go. I used an old panorama sitting on my computer.....the abrupt line is because one side of the pano was land mass and the other side was the ocean. Now that I see how they work, I'll compose with this in mind.....that the opposite sides will meet.
The app makers actually suggest that you shoot (or choose an existing photograph) a) with sides that are identical, or nearly so, and b) that are panorama (so shoot panorama, or panorama-ise an existing shot, which is what I did with the first.
I'm pretty much grounded at the moment, so have only been using existing shots.