Интернет-эквайринг. Не удается получить данные от банка

<?php
 
if (isset($_POST['id']))
 {
 $sum = $_POST['amount']/100;
 $amount = $sum*100;
 $card = $_POST['card_num'];
 $status = $_POST['status_desc'];
 $signature = $_POST['signature'];
 $order_number = $_POST['order_number'];
 $av_sign = *****;
 $shop_id = ****;
 $signature_check =  strtoupper(md5(strtoupper(md5($av_sign).md5($shop_id.$order_number.$amount))));
 if ($signature = $signature_check)
 {
 echo "Платеж $sum рублей
Статус: $status
";
 }
 }
 
?>

$logfile=fopen('test.log','w');
foreach ($_POST as $key => $value)
{
   $msg = 'параметр '.$key.' имеет значение: '.$value."\n";
   fwrite($logfile,$msg);
}
fclose($logfile);

$db_host = 'localhost';
$db_name = '***';
$db_username = '***';
$db_password = '***';
$db_table_to_show = '***';
 
$connect_to_db = mysql_connect($db_host, $db_username, $db_password)
        or die("Could not connect: " . mysql_error());
 
    mysql_select_db($db_name, $connect_to_db)
        or die("Could not select DB: " . mysql_error());
 
mysql_query("UPDATE payment SET sum = '$amount' WHERE order_number='$order_number'");
mysql_close($connect_to_db);

http_response_code(202);

header("HTTP/1.1 202 Accepted");