In-App Subscription

Hi, I have a problem with StoreKit regarding in-app subscription purchases. When I upload the app to TestFlight and during the review process, it doesn’t work on a real device. However, it works fine on the simulator. I get the error: "Subscription unavailable" (see image). Does anyone know what might be causing this and how to fix it? Please help!

In-App Subscription
 
 
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