I’m not actually able to load that page in a browser. Pulling it via curl does succeed, but the page only appears to contain a header with some meta tags. The tags look valid, so I’m not sure why Twitterbot (our cards agent) isn’t able to retrieve them.
Documentation on Cards is available on our developer website. This details how to setup your meta tags, and it looks like you’ve done that. If your page was successfully submitted to the validator, you’d then be able to apply to have the card verified.
I’m not certain why the validator is failing to retrieve your page but I suspect something is going on with your server?
Your twitter:image:src tag contains
Trying to load that in the browser presents an image which implies that maybe something is not configured correctly either?