Updates a voicemail box in place; supported fields you omit keep their current values. voicemail_options and voicemail_destinations are replaced wholesale by whatever array you send, and an empty array clears them, while voicemail_greetings is applied entry by entry according to each greeting_action rather than replacing the set. The mailbox keeps its own account and number: account or mailbox identifiers in the body, such as domain_uuid, voicemail_id and voicemail_uuid, do not retarget it. Authorization failures are reported as 400 rather than 403, and the child records are written after the main settings, so one of them can fail once the settings have already changed.