When painting plastic and to prevent the paint from peeling on the plastic first wash the plastic surface off with some mild soap and water and then dry it off.
Then lightly buff the plastic surface with 220 to 300-grit sandpaper to create a rougher surface on the plastic which will help the paint adhere to the plastic.
After buffing and sanding down the surface of the plastic wipe down the surface with rubbing alcohol and then apply a coat of primer and let the primer dry.
Then use a paint that is made to adhere to plastic for better adhesion of the paint and then it should not peel off anymore.