If you have services that are validating In App Purchase receipts, Apple’s documentation doesn’t clearly state whether you should continue validating those receipts against the sandbox or production environment while the app is in review. The answer is, however, found at the bottom of Technical Note TN2259:

What url should I use to verify my receipt?

• Use the sandbox url https://sandbox.itunes.apple.com/verifyReceipt while testing your application in the sandbox and while your application is in review.
• Use the production url http://buy.itunes.apple.com/verifyReceipt once your application is live in the App Store.

Once your application is approved, you should switch your services over to use the production environment.