Unable to get Twitter Cards to work with Blogger

[delighting_days]

I have Open Graph tags enabled in my blog (http://delightingdays.blogspot.com) and have the following code inserted for twitter cards. However, I’m not able to see any content for the validator and I get a warning that it is not whitelisted. error message is Unable to render Card preview
Code used:

<!-- twitter card details -->
<b:if cond='data:blog.pageType == &quot;item&quot;'>
      <b:if cond='data:blog.postImageUrl'>
        <b:if cond='data:blog.metaDescription'>
          <meta content='summary' name='twitter:card'/>
          <meta content='@delighting_days' name='twitter:site'/>
          <meta content='@delighting_days' name='twitter:creator'/>
          <meta expr:content='data:blog.pageName' name='twitter:title'/>
          <meta expr:content='data:blog.metaDescription' name='twitter:description'/>
          <meta expr:content='data:blog.postImageUrl' name='twitter:image:src'/>
          <meta expr:content='data:blog.homepageUrl' name='twitter:domain'/>
        </b:if>
      </b:if>
</b:if>
<!-- end twitter card details -->

[delighting_days]

Code used

> <!-- twitter card details -->
> <b:if cond='data:blog.pageType == &quot;item&quot;'>
>       <b:if cond='data:blog.postImageUrl'>
>         <b:if cond='data:blog.metaDescription'>
>           <meta content='summary' name='twitter:card'/>
>           <meta content='@delighting_days' name='twitter:site'/>
>           <meta content='@delighting_days' name='twitter:creator'/>
>           <meta expr:content='data:blog.pageName' name='twitter:title'/>
>           <meta expr:content='data:blog.metaDescription' name='twitter:description'/>
>           <meta expr:content='data:blog.postImageUrl' name='twitter:image:src'/>
>           <meta expr:content='data:blog.homepageUrl' name='twitter:domain'/>
>         </b:if>
>       </b:if>
> </b:if>
> <!-- end twitter card details -->