我尝试在我的子主题中添加自定义表单。我已经阅读了此问题的所有文档，但仍然返回0，这是我的代码

作用php（子主题）

function my_custom_scripts() {
  wp_enqueue_script( \'custom-js\', get_stylesheet_directory_uri() . \'/assets/js/custom-child.js\', array( \'jquery\' ),\'\',true );

  //the_ajax_script will use to print admin-ajaxurl in custom ajax.js
  wp_localize_script(\'custom-js\', \'the_ajax_script\', array(\'ajaxurl\' =>admin_url(\'admin-ajax.php\')));
} 

add_action( \'wp_enqueue_scripts\', \'my_custom_scripts\' );
add_action( \'wp_ajax_callbackcity\', \'callbackcity\' );
add_action( \'wp_ajax_nopriv_callbackcity\', \'callbackcity\' );

function callbackcity() {
  extract($_POST);

  $data = \'tes city - \'.$svalue;
  return $data;
  wp_die();
  //die();
}

jQuery("#get_city").on("change", function (e) { 
        
        e.preventDefault(); 
        jQuery.ajax({
            type: \'POST\',
            dataType: \'json\',
            url: the_ajax_script.ajaxurl,
            data: {
                \'action\': \'callbackcity\',
                \'svalue\': 12
            },
            success: function(data) {
                console.log(data);
            },
            error: function() {
                console.log(\'ERROR\');
            }
        });
    });