Dynamic Cards: URL can't be parsed?

Hi,

I’m testing out Ghost locally and I want to use dynamic cards. I want to use dynamic cards, so I clicked the plus sign on a new post to try and see if I could embed content from another site. Upon pasting the URL however, it did not work, as ghost told me that this URL Get Started with Groupon couldn’t be parsed and thus couldn’t be embedded. Anyone know how this works?

Thanks!