CSS selector link on POP up pro

Hi there,
Trying to get the POP up on CSS selector click to work, but can't. Was trying to find an example on the 'usage' tab of the plugin page, but looks like it is an outdated instruction page from a previous version of the plugin.

Can you provide an example of how the css selector code should be placed? Tried several different types, both ID and Class and none trigger it. Must be the way I have it setup I'm sure. Can you advise with some examples, it would be much appreciated. Thanks much!
Mark