Additional url.xml to sitemap index

Hello, maybe i’ve found the solution: i noticed that the rewrite rules have been blocking my custom url, so i used the filter showed below to add my url to the rewrite rules

add_filter( 'rewrite_rules_array', 'addPlacesToRewriteRules', 1, 1 );

function addPlacesToRewriteRules( $wp_rules ) {

    $sm_rules        = array(

        'places\.xml$' => 'index.php?xml_sitemap=params=places',

        );

        return array_merge( $sm_rules, $wp_rules );

    }