Can we test webhooks before our app is approved on the apple app store?

Goal:

We want to test our In-App Purchase Flow end-to-end in TestFlight using a sandbox account and see sandbox data in RevenueCat and receive the associated webhook events.

Problem:

Our app has not yet been approved on the apple app store. It appears I can only provide App Store Server Notifications URLs in the App Store section under App Information. I don’t see a way to add them to a TestFlight build.

Question:

Is there a way to accomplish my goal before being approved on the app store, or is that a prerequisite of receiving webhook events from sandbox IAP transactions?

Thanks!