fb app system: index.php

<?php
require 'config.php';
require_once 'inc/lib/facebook.php';
require_once 'inc/fb.php';
echo '<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>';
echo APP_NAME;
echo '</title>
<link rel="stylesheet" type="text/css" media="screen" href="';
echo URL_APP;
echo 'page/css/style.css" />
<script src="';
echo URL_APP;
echo 'page/js/jquery.js" type="text/javascript"></script>
<script src="';
echo URL_APP;
echo 'page/js/ajax.functions.js" type="text/javascript"></script>
</head>
<body>
    <script type="text/javascript" src="https://connect.facebook.net/en_US/all.js"></script>
    <script type="text/javascript">
        FB.init({ appId  : \'';
        echo APP_ID;
        echo '\', status : true,  cookie : true,  xfbml  : true  });
        var page_app = \'';
        echo PAGE_APP;
        echo '\';
        var url_app = \'';
        echo URL_APP;
        echo '\';

        var liked = \'';
        echo ($liked)?1:0;
    echo '\';
    </script>
    <div id="fb-root" class="fb_reset"></div>
    <div id="container">';
if ($liked != true)
{
//=================================================== PAYMENT ====================================//