Propeller Ad rejected "We are unable to see the landing page (destination URL is not accessible)"

Newbie question - I'm using a lander to collect emails and then on submit, redirect them to an affiliate offer. My ad was rejected because they are unable to see the landing page (destination URL is not accessible.) Is there a way to get around this? How can I make the link accessible to Propeller Ads so the campaign is approved, while also collecting emails, as