I have used summary cards before for my blog and they worked, but for the past few months I have had problems with it saying 'Not Whitelisted'.
My blog is www.millennialrants.co.uk
I have entered code in my post I am trying to share currently (http://www.millennialrants.co.uk/2017/01/tips-for-attending-your-first-blogger.html), and the card validator says:
INFO: Page fetched successfully
INFO: 10 metatags were found
WARN: Not whitelisted