When using the tracking pixel method in conjunction with a secure certificate you'll need to make sure the tracking pixel is being called securely with https rather than http.  If your pixel is being called on a secure page (https) and is not calling https in the pixel, the browser will either produce a popup asking if the customer wants to display insecure items or it will be ignored altogether depending on the browser settings.

URL Setting In Your Cart Admin Center
Simply change the URL setting to use https instead of http.

Integration Code In A File
Simply change the URL setting to the sale.php file to use https intead of http.

In order for this to work you must actually have a secure certificate located where iDevAffiliate resides.