Question regarding new payment plugin

-- HikaShop version -- : 2.3.3
-- Joomla version -- : 3.3.6

Hello,
I am developing a payment plugin for a bank's payment gateway from the example one offered in the Hikashop site.
The problem comes at the moment of receiving the gateway's notification of the payment. The bank requests a "response to a notification" as "a URL-coded document which only contains one text line (no HTML tags, etc.) in the format parameter=value". This parameter is the url for the user to be redirected.

If I kill the application right after echoing such line, the redirection works out fine:

function onPaymentNotification(&$statuses)
	{
	...
	else //If everything's OK, order is validated -> success
		{
			$this->modifyOrder($order_id, 'confirmed', true, true);
			$requestURL = "rurls=".HIKASHOP_LIVE."index.php?option=com_hikashop&ctrl=checkout&task=after_end"; // successful transaction 
			echo $requestURL;
			exit;
			// return true;
		};
	}