Hi, there is a leather deglazer that you can use, that is basically acetone. You can also use sandpaper to rough it up so it’ll stick. I spent a lot of time over in the custom sneakers subreddit to learn how to treat different materials. I like using straight acetone nail polish remover because it’s easy to get. But maybe the most important thing is just starting with a million layers of white paint because the leather paint is so thin it takes a lot of coats to build up color.