I tried to paint over a metal door going to my garage. I did not sand it and the paint can be easily scraped off with my fingernail. How to I remove the paint and what are the right steps?
If you have available a not-so-high-pressure washer, use that. This is the simplest way to remove the offending coat.
From your description, seems as though you applied an acrylic coating over an alkyd coating. I would suggest for best results after removal you sand lightly, prime with a bonding primer and then repaint with an acrylic coating.