You can make any image or text on any Stacks page on your site a link to open the PaySnap cart. Begin by adding the PaySnap Base stack to any page that should contain a view cart link. Note that PaySnap Base should be configured identically among all pages on your site.
To create the link all you need is to use a simple HTML link or the RapidWeaver link tool to add the proper attributes. You will need to give the link a “class” with a value of “paysnap-viewcart”. Here's how you'd accomplish this with the RapidWeaver link tool: