Can’t Remove Center Hub Nut From Trailer

Trailer question - remove if you feel it’s not sunfish oriented enough, but I am struggling to remove the center nut from the hub on my sunfish trailer. Anyone have any ideas? Thought it might have reverse threading so I’ve tried both directions but it will not budge. Everything I’ve googled just tells me how to remove dust caps but I don’t think this is a dust cap.

What am I missing?