When trying to use the validator against http://www.libreriausados.com.ar/Libro-Usado/Guy-des-Cars-El-fabricante-de-muertos-0004.html I get the WARN: Not whitelisted error and the card preview can’t be rendered.
The page contains the og:description, og:title and og:image tags, as well as allowing Twitterbot in the robots.txt file.
Is there any way to further diagnose this issue? On Facebook for example the OpenGraph information is parsed correctly.