Sandbox and production URL while testing my app (reject by the app review team)

I have in-app purchases (consumable) in my game and when the payment is successful, the receipt is forwarding to the server to validate the receipt. It works well when I test it in the sandbox.

I’m trying to pass the apple review process but can’t because they reject me because the validation is not working. (Guideline 2.1 - Performance - App Completeness)

But the problem is that it’s working! I have dug into the logs and decoded the receipts and see they use the sandbox environment.

Seriously? How it can be the truth? I thought they test it in the production environment.