Issues accessing administrative nextcloud account

First off, I apologize if this has been answered previously, I did some searching around and didn’t find much of anything.

Today I joined UCS to a quite fresh AD Domain (about 3 hours old, almost nothing changed from defaults). From my understanding, I need to log into Nextcloud as the domain administrator account, but that isn’t working for me, I just end up with a wrong username or password error. I’ve tried other accounts that are in the domain admins group, however they just have standard user permissions.

Am I doing something wrong here or does the app act funny when UCS is operating as a server joined to a domain rather than a DC?

Any help would be much appreciated!