Integrate facebook credits in facebook apps

I want to Integrate facebook credits in my fb apps. I downloaded sample code from referral site but that is not working.

My app link is apps.facebook.com/football_leagues and from fan$ link when you click at redeem , a popup window opens for credits. But I get an error message:

There was an error making your Facebook Credits purchase. Ord开发者_如何学Cer::update_order called with invalid state transition:3 -> 0

The documentation is here: http://developers.facebook.com/credits and there's a sample (PHP) application included with the SDK. The sample application can be retrieved from github here: https://developers.facebook.com/docs/creditsapi/

The technical docs are here: https://developers.facebook.com/docs/creditsapi/