PopUp Pro On Specific URL Not working as expected?

Hey Guys,

I've been having some issues with PopUp Pro's On Specific URL feature. For example, I'd like the pop up to show on two pages. The main page..


And a second page..


Unfortunately it doesn't seem to load on the latter, which seems to be because of the parameter ?page_id=2. I've searched for clues to why this might be, but it seems this isn't much of an issue for others.

I'm using WordPress 4.0, Twenty-Thirteen theme. I've tried disabling all other plugins, messing with settings and code, but haven't had much luck. Any help would be appreciated!