/** add custom post types to archive pages **/
add_filter('pre_get_posts', 'query_post_type');
function query_post_type($query) {
  if ( is_category() || is_tag() && empty( $query->query_vars['suppress_filters'] ) ) {
    $post_type = get_query_var('post_type');
    if($post_type)
        $post_type = $post_type;
    else
        $post_type = array('post','events','testimonails','client','services','backstage'); // replace cpt to your custom post type
    $query->set('post_type',$post_type);
    return $query;
    }
}