回发脚本不起作用

Question

我正在运行每次转化费用网站，并且需要通过我的网站即时跟踪我的用户完成的优惠，但我使用的回发脚本无法正常运行，因为它不会更改数据库中金额的值。以下是剧本：

<?php 

$dbhost = 'host';
$dbuser = 'user';
$dbpass = 'pass';
$dbname = 'name';

// 2. Create a database connection
$connection = mysql_connect($dbhost,$dbuser,$dbpass);
if (!$connection) {
    die("Database connection failed: " . mysql_error());
}

// 3. Select a database to use 
$db_select = mysql_select_db($dbname,$connection);
if (!$db_select) {
    die("Database selection failed: " . mysql_error());
}

$subid = $_REQUEST['subid'];
$amount = $_REQUEST['payout'];

mysql_query("UPDATE users SET amount=amount+".$amount." WHERE id='".$subid."'");

   echo "<b>Amount Credited:</b> Rs ".$amount.";      

?>