Today, my app was rejected for the exact same reason on the exact same device and OS. Interestingly I have also seen "You are not authorized to make purchases of this InApp in Sandbox at this time. This Apple Account doesn’t have permission to make In-App Purchases." on a testflight version of another app of mine that is already approved and live on the store. I don't know the answer to the question or how to solve it right now, but I am trying to debug and hope to have something soon.

They've stopped sending those emails. There should be an email titled "The status of your (iOS) app, [App Name], is now "Waiting for Review""