If you want to use the embed code as third party creative on DoubleClick for Publishers there are a few steps to take in order to have the clicks tracked correctly:
1. First, copy the embed code from My banners page.
2. On DFP click on Add creative then select the Third party option. Before pasting the embed code make sure you add this line to it: clickTag=%%CLICK_URL_ESC%%http://www.yoururl.com
That line needs to be added between the & sign and the width value like this:
<iframe src="//cdn.bannersnack.com/banners/xxxxxx/embed/index.html?userId=xxxxxxx&t=xxxxxxxx&clickTag=%%CLICK_URL_ESC%%http://www.yoururl.com" width="728" height="90" scrolling="no" frameborder="0" allowtransparency="true" allowfullscreen="true"></iframe>
3. If you add it correctly on the right panel you should see a notification that the macros have been inserted and you can click Save.
Here's a short tutorial that shows how to do it: