Why is my Add a New Property Button Grey-ed out?

Hi all!How should I set up a test where the landing page I'd use, let's call it a "thank you" page, would always have some dynamic query string parameter? For example, domain.com/thankyou?offerid=12312312312. The offerid could be different, but i just want to track how many times someone got to /thankyou. Target only seem to track the "conversion" when the URL has the query string parameter in it. Thanks in advance for the help!