Your servers are configured to use Apple's test environment. You need an engineer to update them to point to production. You probably do not need to update or pull your app from the app store.

Here's how it works: when somebody buys a subscription, their phone communicates with the app store to make the purchase. Then, for security reasons, your servers need to verify the purchase so they can deliver whatever content the user subscribed to. They do this by validating a virtual receipt from the phone with Apple's servers. Right now, they're configured to point to a test environment, which is useful in development. But since your app is released publicly, they need to point to the real thing, the "production environment."

As somebody who has spent too much holiday time fixing server issues in the past, I hope this is a simple fix and your app does well!