Will acrylic paint stick to a shiny iphone case?

It is some sort of shiny case (not plasticy but not metal either) I have no idea what it is but it's a bit shiny, so I sanded it. Will the coat of paint I'm putting on it stay? Even after sanding it was still shiny.

Really impossible to answer. Only way to know is to do just what you've done… Give it a try.