Trigger: Form filled out on a non-marketo webpage?

Hi There!

We are implementing a set of non-marketo landing pages into which we've embedded marketo forms. I'd like to use a "Fills out form" trigger with a constraint that the form is filled out on the specific web page's URL. This is necessary because we will be re-using the form for multiple pages.

When I try to manually enter the URL, however, I get a red squiggly line, and an error saying the URL is invalid  (prntscr.com/enp2t2) (prntscr.com/enp5d1).

How can I make this work? We have installed the marketo tracking cookie in our site but can't figure out how to make the form work.

Eric