Unable to log into new Windows server

Hi, I seem to always get a message that says “The username you have entered is not enrolled with Duo Security.”, I have seen this message documented in various places, however there is no actual answer on how to get around this. I have set username normalisation to None, which has made no difference. all I want to do is just have a local user, and prompt on my phone when i try to log in with it. I don’t quite understand the whole enrol users thing, I have enrolled myself despite being the admin, using the same username as the local account on the server, and it still just instantly giving me that message. Is there something I’m missing?