I can't seem to get the Twitter Card to validate on http://poweredbyfacts.com - the metadata's been added correctly, it appears, via "All-in-One-SEO" plugin (wordpress), and scan of the page source code. Just keep getting "ERROR: Fetching the page failed because the request timed out." - though one time, when using "http://www.poweredbyfacts.com", it seemed to recognized the metadata, then the redirect, and then a "not whitelisted" message...but only once, never again. The site performance is OK.
WITH a trailing slash (http://poweredbyfacts.com/) I get:
INFO: Page fetched successfully
INFO: 8 metatags were found
WARN: Not whitelisted
But still can't render the card preview.