I’m not familiar with jekyll-seo-tag - I took a quick look at the docs on Github and it seems to suggest that the Twitter Card tags will be added automatically. However, none of them appear in your site’s source code, I only see a few og: tags and no twitter:card markup.
As @ePirat says, the “not whitelisted” error is misleading (and would only apply if you had a video player card), basically the problem here is that your site doesn’t have any Cards markup to enable us to validate or render a card for you.
