Metabox Not Showing on Custom Post Type But On Pages and Post

I have a Custom Post Type like

function cpt_Projects() {
    $labels = array(
        'name'                 => 'Projects',
        'singular_name'        => 'Project',
        'menu_name'            => 'Projects',
        'name_admin_bar'       => 'Projects',
        'parent_item_colon'    => 'Parent Projects:',
        'all_items'            => 'All Projects',
        'view_item'            => 'View Project',
        'add_new_item'         => 'Add New Project',
        'add_new'              => 'Add New Project',
        'new_item'             => 'New Projects',
        'edit_item'            => 'Edit Project Item',
        'update_item'          => 'Update Project Item',
        'search_items'         => 'Search Project Item',
        'not_found'            => 'Project Not found',
        'not_found_in_trash'   => 'Project Not found in Trash',
    );
    $args = array(
        'label'                => 'ProjectsCPT',
        'description'          => 'This Post Type Adds Eyeglasses to Website',
        'labels'               => $labels,
        'supports'             => array( 'title', 'thumbnail', 'editor'),
        'taxonomies'           => array( 'ProjectsTax' ),
        'register_meta_box_cb' => 'add_details_metabox',
        'hierarchical'         => true,
        'public'               => true,
        'show_ui'              => true,
        'show_in_menu'         => true,
        'show_in_nav_menus'    => true,
        'show_in_admin_bar'    => true,
        'menu_position'        => 5,
        'can_export'           => true,
        'has_archive'          => true,
        'exclude_from_search'  => false,
        'publicly_queryable'   => true,
        'capability_type'      => 'post',
    );
    register_post_type( 'ProjectsCPT', $args );

}

add_action( 'init', 'cpt_Projects', 0 );

and a Metabox like

  function add_details_metabox($post_type) {
    $types = array('post', 'page', 'ProjectsCPT');

   if (in_array($post_type, $types)) {
      add_meta_box(
        'details-metabox',
        'Project Details',
        'detail_meta_callback',
        $post_type,
        'normal',
        'high'
      );
   }
  }

after running the code the Metabox is showing on all Pages and Posts but not on Custom Post Type ProjectsCPT Can you please let me know what I am doing wrong? (It works fine if I remove the if statement

 if (in_array($post_type, $types)) {}

but this add metabox to all Posts and Pages which is not what I need to do

Post type names cannot contain capital letters. So behind the scenes, your CPT is probably called projectscpt rather than ProjectsCPT – hence it not matching the value in your array.