DEVILBOX_UI username

What’s the DEVILBOX_UI username and where is this documented? I tried my login username along with admin & root but none of these work.

Looks like the username is devilbox but I did not see where that is documented. It should be documented in the sections describing the devilbox UI e.g. in:

Is there any way to change this username?

There is currently only a setting to change the password.