How can I make my metabox appear?

I’ve managed to make it work because of @howdy_mcGee’s comment. I did not notice that I had to call the specific post type name of it. my code is now like this and it shows up!

    function slide_add_post_meta_boxes() {
  add_meta_box(
    'pukkemukslideshow',      // Unique ID
    __( 'Slideshow', 'example' ),    // Title
    'slide_post_class_meta_box',   // Callback function
    'slideshow',         // Admin page (or post type)
    'advanced',         // Context
    'high'         // Priority
  );
}