php - moodle paypal - send paid amount to included page after purchase -

i'm trying include affiliate sales-pixel "enrol/paypal/return.php" in moodle paypal plugin. need track sale pay out affiliates.

i've included in "return.php"with

require_once(dirname(__file__).'/checkout-tag.html'); 

the sales-pixel looks this:

<script type="text/javascript" src="https://ad.zanox.com/pps/?xxxxxxxxxxxxxxxmode=[[1]]   &customerid=[[<?php echo $user->username ?>]]   &orderid=[[<?php echo $user->username ?>]]   &currencysymbol=[[eur]]   &totalprice=[[<?php echo $cost ?>]]"> </script> 

the username , currency symbol transmitted fine. totalprice transmits no value.

can me read out paid amount , transmit through pixel?