Unable to render Card preview using Twitter Card Validator
I came across an issue when trying to validate Twitter Cards using the Twitter Card Validator. The site uses WordPress with the WordPress SEO plugin by Yoast and although both were set up correctly, the Twitter Card Validator was returning a Unable to render Card preview error.
After speaking to my hosting provider, it was discovered that this was being caused by the server’s ModSecurity Firewall. After this rule was whitelisted on the firewall, it worked. Hope this helps anyone who is having the same problem.