The current workflow makes it ~impossible to figure out why certificates you upload are not being accepted.

Upload your new certificate / key files via the Web UI:

And then you get this error message:

It would be really helpful if there was a more thorough error message that gave some clue as to what was wrong with the file... Format? Some aspect of the key?

Logs in the UI would be amazing, but even if it got into the diagnostic system logs that can be downloaded in the Maintenance tab, that would also be super helpful.