Ask HN: Why am I getting 402 Payment Required on HN?

I recently launched a Hacker News app for Windows Phone and now my API is getting 402 Payment Required from Hacker News. The API is using the exact same code as @cheeaun's http://node-hnapi.herokuapp.com. I merely cloned his API and deployed it to my own Heroku instance, to avoid using up his bandwidth.

Any idea why this is happening? I find it odd that Hacker News would be returning a 402 if they decided to block my app as opposed to 401/403.