How to make Panel Page variant selection rules detect URL parameter? On D7 I have set up a new panel page variant and want to use it with a certain selection rule:

 String: URL path   Current path is "*/cars/*?buy"


Eg I want this panel variant to be used if the URL is new/cars/honda?buy.

However the above doesn't work. Adding ?buy to the url doesnt trigger it to be used.

Would anyone know a way to set selection rule so that I can use this page variant with a give parameter in the URL?
I found the Selection Rule Query string exists does this.