Ephemeral Single Onion Services must have the NonAnonymous ADD_ONION flag

Tor checks that the flag matches the configured onion service anonymity.

Tor refuses to create unflagged onion service using ADD_ONION, if they
would be non-anonymous. The error is:
512 Tor is in non-anonymous onion mode

Similarly, if the NonAnonymous flag is present, and Tor has the default
anonymous onion config:
512 Tor is in anonymous onion mode