Bug with register_post_type(order)

https://codex.www.ads-software.com/Reporting_Bugs

You can still register the post type with :

register_post_type( 'my_order',
		array(
			'labels' => array(
				'name' => __( 'Order' ),
				'singular_name' => __( 'Order' )
			),
		'public' => true,
                'rewrite' => array('slug' => 'order')

		)
	);

This will show the post type as “Order” in the wp-admin and use “order” in your urls.