If you saw an error such as
Error 503 Backend fetch failed or received a blank page after an attempted upload, this is typically due to connectivity issues somewhere between you and Fireside’s infrastructure. It might be due to a slower connection on your end, or just trouble somewhere in between.
Unfortunately, it is essentially impossible to determine where or why the issue has occurred. Fortunately, this error usually resolves itself if you wait a short while, or try from a different location, so waiting and trying again later is your best action.