Henrik, you must kill the gloss BEFORE spraying paint. That is a hard surface. You can scuff all surfaces with an ultra-fine Scotch-brite pad...or, better yet, wet sand all parts to be painted with some 1000 grit paper. Using a drop or two of dish-washing soap...that does not contain silicone... to a liter or so of water will help the paper glide over the surface you are sanding. Go gently and take your time. Allow the parts to dry thoroughly and check for any areas that are still shiny.
Before you start sanding, use a quality Paint Prep solution and was all parts thoroughly to remove any wax or silicone. Those contaminate will cause the new paint to fish-eye.