Custom DB insert after payment confirmation

[qwerpoiu338]

Greetings,

I'm trying to insert paypal_ipn_id and some other variables into a custom table on the Paypal payment is completed. But nothing gets inserted in the custom table.
Assuming the correct way to do is to define custom table in the database_tables.php file and use the defined name in the paypal.php file shown below:

function after_process() {    
global $insert_id, $db;    
if ($_SESSION['paypal_transaction_PDT_passed'] != true) {      
$_SESSION['order_created'] = '';      
unset($_SESSION['paypal_transaction_PDT_passed']);      
return false;    
} else {      
unset($_SESSION['paypal_transaction_PDT_passed']);      
$sql = "insert into " . TABLE_ORDERS_STATUS_HISTORY . " (comments, orders_id, orders_status_id, date_added) values (:orderComments, :orderID, :orderStatus, now() )";
      $sql = $db->bindVars($sql, ':orderComments', 'PayPal status: ' . $this->pdtData['payment_status'] . ' ' . ' @ ' . $this->pdtData['payment_date'] . "\n" . ' Trans ID:' . $this->pdtData['txn_id'] . "\n" . ' Amount: ' . $this->pdtData['mc_gross'] . ' ' . $this->pdtData['mc_currency'] . '.', 'string');
      $sql = $db->bindVars($sql, ':orderID', $insert_id, 'integer');
      $sql = $db->bindVars($sql, ':orderStatus', $this->order_status, 'integer');
      $db->Execute($sql);

 $var2 = 1;
 $var3= 0;
 $var4 = 0;

      $sql = "insert into " . TABLE_SUB_LIST . " (mem_id, field2, field3, field4) values (:ipnid, :var2, :var3, :var4)";
      $sql = $db->bindVars($sql, ':ipnid', $this->paypal_ipn_id, 'integer');
      $sql = $db->bindVars($sql, ':var2', $var2, 'integer');
      $sql = $db->bindVars($sql, ':var3', $var3, 'integer');
      $sql = $db->bindVars($sql, ':var4', $var4, 'integer');
      $db->Execute($sql);

 ipn_debug_email('PDT NOTICE :: Order added: ' . $insert_id . "\n" . 'PayPal status: ' . $this->pdtData['payment_status'] . ' ' . ' @ ' . $this->pdtData['payment_date'] . "\n" . ' Trans ID:' . $this->pdtData['txn_id'] . "\n" . ' Amount: ' . $this->pdtData['mc_gross'] . ' ' . $this->pdtData['mc_currency']);
    }
  } 

What did I do wrong? Please help.