I have never been able to upload courses that I have downloaded, from anywhere, GPX, or TCX, into the garmin connect web app. I just get "An error occurred with your upload. Please try again." I have dragged and dropped, and clicked browse and uploaded them from my downloads folder. Please help! I know I can drag and drop into my "new files" folder, but I would like the connect app to work as well.
You have written two different things;
I can't upload to GC
I can't upload to the 820
To upload to the 820 use the ConnectIQ app RouteCourse.
Thanks for the mention TrippyZ.
Note that with routeCourse you don't even need to use Garmin Connect at all--just create or import the route into our https://dynamic.watch route management website and start the routeCourse app on your Edge to lists and download your routes to it.