I am passing URL parameters from an external advert into the Unbounce Landing Page, which pre-populates a hidden field. However when the user fills out the form, and submits it, I get an error, as the URL is still passing the parameter in addition to the Post Form Data to a URL.

Once a user gets to the landing page, how can I then strip it out of the URL it passes as a part of the Post Form Data to a URL?

Example:

www.landingpage.com/?source=123 (Incoming URL)

www.landingpage.com/ (Outgoing URL)

Thanks