WordPress Custom Post Type Not Appearing In Backend

I’ve just experienced a problem when working on a WordPress website whereby I registered a custom post type in functions.php, however I could not get it to display in the left hand navigation. I received no errors at all, the post type would just not display.

My code was as follows:

add_action( 'init', 'create_post_types' );
function create_post_types() {
	register_post_type( 'homepage_large_panels',
		array(
			'labels' => array(
				'name' => __( 'Homepage Large Panels' ),
				'singular_name' => __( 'Homepage Large Panels' )
			),
		'public' => true
		)
	);
}

The Solution

After a bit of trial and error, plus further research, I found the following snippet from the WordPress documentation:

$post_type
(string) (required) Post type. (max. 20 characters, can not contain capital letters or spaces)
Default: None

The $post_type parameter I was using in the code above was 21 characters long so, after changing it to something less than 20 characters, it began to show immediately.