To know if you're in sandbox environment or not, you can have a look at the purchase popup. If you can read "[Sandbox environment]" at the bottom, then it means you're using the sandbox. Otherwise, you're using the real Appstore (But I'm pretty sure it's not the case since this is automatically chosen by the device).
Anyway, it seems that Apple Sansbox environment is experiencing some problems today. For example, I have an app that was dealing correctly with inapp purchase yesterday. Today, only retrieving SKProducts was ok.
I recommend you to be patient until the problem is fixed by Apple.