我得到了这个错误

致命错误：未捕获错误：在/home/stageidg/public\\u html/idg/wp-content/themes/idg-child/secondmenu中调用未定义的函数wp\\u nav\\u menu（）。php：2堆栈跟踪：#0{main}抛出/home/stageidg/public\\u html/idg/wp-content/themes/idg-child/secondmenu。php在线2

php文件中的第2行是：

wp_nav_menu( array(\'menu\' => \'Services\', \'theme_location\'=>\'services\' ) );

$.ajax(
{
url: "http://example.com/idg/wp-content/themes/idg-child/secondmenu.php", // path to your PHP file
dataType:"html",
success: function(data)
{

   $(data).appendTo(inner_overlay); // load-into-div is the ID of the DIV where you load the <select>

} // success
}); // ajax