I have all that but plate does not flatten. Door opens and closes, just looks wonky.Normally there is a hinged plate at the top of the door that gets locked once in place, when not locked there is ample 'play' to raise the top part of the door and stab into the bottom. Once in the top of the door swings in place and is locked into place via turn buttons on the roof's short side wall, they fit through holes or slots in the hinge plate, once the turn buttons are turned they lock the hinge plate against the roof's short side wall.
Found this image here of a hinge plat with missing turn buttons
https://www.popupportal.com/media/door-top-hinge.9391/