While trying to remove a domain from my cloudron server, I clicked remove and nothing happened. I clicked a few times, refreshed the page, etc. No error, no confirmation.
Looking at the browser logs, my server was throwing a "409 Conflict" error message in console, but never telling me anything.
Long story short, I still have a mailbox left under the domain (even though email services disabled) and needed to delete that before continuing.
My suggestion is that when an error occurs in cloudron's admin UI due to a user action, an alert should come up. In this case it could have just said "Domain is still in use." or something like that.