Changing default slug listings

Hi Simon

Thanks for great plugin. Im trying to change listing slug using this code bellow:

/**
 * Custom listing slug
 */
add_filter( 'wpsight_rewrite_listings_slug', 'my_rewrite_listings_slug' );

function my_rewrite_listings_slug( $slug ) {

	$slug = 'custom-slug';

	return $slug;

}

Updated both polylang and wp permalinks structure, but slug is still listings.
My setup is WP 4.6.1, Theme oslo, im missing something simple just unable to see it