How to add tracking code of shareasale

I need add tracking code of shareasale on my website. But have no any tech support for opencart on shareasale. Now shareasale has a code:
<img src="https://shareasale.com/sale.cfm?amount= ... ntID=46265" width="1" height="1">

They said need put this code on "Thank you" page, but I tried it on success.tpl under /catalog/view/theme/XXXX/template/common/. But it did not work. If need to modify success.php? If yes how to modify?
Or if need modify other page?

Please help me, thank you very much!

The phrases "Thank You" page and "Checkout Success" page are often used interchangeably. First make a backup copy of success.php then paste the code in with NO extra spaces before or after the < .... >

Merry