I am not with Laminar Research; just a flight simmer.
At my age I am of the "old school" as I am not one to use the "cloud" system ie Onedrive so I don't know a lot or anything about it.
What your dilemma suggests to me is that in placing the software into onedrive and then into the recycle bin it has left some "traces" of X-Plane somewhere on your PC linked to the cloud.
I respectfully suggest you go for a Dr Google search for HTTP error 503 to ascertain what the error is all about and possibly download software to remove the problem provided you do not have a decent software package removal tool. I did a search and found the following at http://www.wiki-errors.com/err.php?wiki=503&gclid=EAIaIQobChMIicvdwKPx3QIVxAQqCh0dAgkAEAAYASAAEgLGcvD_BwE in WIKI-Errors.
When you are convinced the problem has been "fixed", attempt the demo download again. Make sure you have full control of the download dictating where the x-plane software is to be located on your PC either on the desktop or a dedicated drive. Definately not in Program files or allow the download to proceed automatically
Hope it works for you.