Hi,
see the tips here https://forum.nomachine.com/topic/user-for-instant-access#post-52574 and here https://kb.nomachine.com/AR03S01118. Go to the section for Windows, just below figure 2.
I’ll post here for convenience
1) User Principal Name: <username>@<domain> – so you can use this. If you are not able to, please tell us what error you are seeing when trying to promoted to authenticate on the target Windows machine
2) Down-Level Logon Name: <domain>\<username>
3) Short format name, just ‘username’, domain is implicit.
This is not really a different format, since it is just the Down-Level Logon Name without the domain part.