How Do I Paint Steel Doors
OK since you have a mess, get some xylene at the hardware store. OUTSIDE..put down same cardboard and set the door on it. With a brush...brush the xylene over the door and use the solvent to wash the paint off. This will take a while.
Clean it off with a rag. When it dries, scuff sand the door with some scotch brite or #220 sandpaper. Prime the door with exterior acrylic primer. Make sure that you buy a GOOD brush not a $5.00 cheapie. Also by some latex paint conditioner to add to your top coat.