Unable to render card preview



We’ve followed the proper steps to create our Twitter card: we added the meta tags on our site, filled all the fields in https://dev.twitter.com/docs/cards/validation/validator and we can see the preview correctly. However, when we click on “Validate & Apply” and enter our URL, we get this error message: “unable to render card preview”.

Are we missing anything? Is there any way to fix this?

Thanks in advance.