It has since remediated itself, without any environment change (OS, server, and client). Therefore, I err on the server requiring some time to initialise its CalDAV server after account creation. If so, the URI shouldn’t be available during that time period. Should I create a server issue? Unfortunately, I lose my access to the free trial in P1D, but I suppose that if the server version increased, I’d need to create a new account to confirm this regardless.