During Apple subscription renewals in the sandbox environment, why isn't Apple's server sending the server-to-server notifications to our backend?

We're using StoreKit for in-app purchases on iOS, and our backend has the server notification URL configured. However, during subscription renewals, Apple's server doesn't send any requests to our endpoint. What could be causing this?

During Apple subscription renewals in the sandbox environment, why isn't Apple's server sending the server-to-server notifications to our backend?
 
 
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