Google RTDN not receiving events in production

I have developed a Unity app for Android devices, which uses Unity IAP for in-app purchases. I published it in the Google Play Store and it's now currently in production and working. The app itself manages the purchase trough Unity IAP, and when the purchase is completed trough it, the app sends the Google Receipt to my server which then sends and verifies it via Google API, to activate the purchase on my server.

Everything is fine so far.

Now, I have configured a Pub/Sub by setting up a Topic Name and a Subscriber that pushes messages to a custom url on my server, and then I added the full "Topic name" in the "Monetisation setup" -> "Google Play Billing" section of my app. By pressing the "Send test notification", I correctly receive the notifications on my server. However, when a customer really buys an "In-app" product, I don't receive any notification at all.

Someone has any idea why?