Blockchain Receive Payments API v2 Callback

//implementing the callback file

$secret = "your_secret";

if($_GET['secret'] != $secret)
{
  die('Stop doing that');
}
else
{
//update DB
$order_num = $_GET['invoice'];
$amount = $_GET['value']; //default value is in satoshis
//$amountCalc = $amount / 100000000; //optional convert to bitcoins
   $queryUpdate = "UPDATE orders SET paid = 1, recd = $amount WHERE orderid = '$order_num'";
   $doUpdate = mysqli_query($conn, $queryUpdate) or die(mysqli_error($conn));
   echo "*ok*"; // you must echo *ok* on the page or blockchain will keep sending callback requests every block up to 1,000 times!
}