Why doesn't my twitter card work?

[AffinityGabe]

I have my domain white-listed and my meta tags validated, but my tweets aren’t showing cards…

You can see some tweets here that should be showing cards, but are not: https://twitter.com/AffinityGabe

The links are to http://my.affinity.is/volume-12

[andypiper]

Hi Gabe!

Works for me -> https://dl.dropboxusercontent.com/u/1312244/IMG_0081.PNG

Remember, this card type only shows up in the Twitter Android and iOS clients, as stated here in the docs:
https://dev.twitter.com/docs/cards/types/app-card

Also, you might want to take a look at the metadata tags you are including, as several are not valid / recognised / needed, such as twitter:app:name:iphone