Hi,
"echo" is a PHP function and you code is not in a PHP block so it could not work properly.
The "after_end" view have already the order is in content, so you can use this code:
<?php
$app = JFactory::getApplication();
$app->enqueueMessage( JText::_('THANK_YOU_FOR_PURCHASE') );
?>
<!-- Offer Conversion: BellaBuy ATD CPS -->
<iframe src="http://allthedealsaustralia.go2cloud.org/SLe?amount=<?php echo $this->order->order_full_price; ?>&order=<?php echo $this->order->order_number; ?>" scrolling="no" frameborder="0" width="1" height="1"></iframe>
<!-- // End Offer Conversion -->
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.