If the URL doesn’t contain any whitespaces - it returns the expected user object. If there is a whitespace in the URL (which happens if the user doesn’t have an email set, but does have a set RealName, the example would be https://MY-RT/REST/2.0/user/John Doe) - it returns 404. Searching for numeric ids (like [{"field": "id", "operator": ">=", "value": 12345}]returns just the list of all users.