We are getting HTTP 404 when trying to download the certificate for validating the receipt. I've seen two different URIs to fetch the certificate, of which the other is a redirect to the first one. Below is the supposed URI to the certificate:
Certificate with id: A656B9B1B3AA509EEA30222E6D5E7DBDA9822DCD
The address should be fine as I'm able to download another certificate with a different id mentioned here (id: b809e47cd0110a4db043b3f73e83acd917fe1336)
My guess is, that this is due to our app being a beta app at the moment and since I can find the same certificate id from the example receipt in this sample here, but haven't been able to verify it.
Edit: the in-app products are also free at the moment if that matters
This was a bug, as the Beta certificate was never deployed to the server. I have worked to get that added and now you should be able to use the sample code, as is, and download the certificate without receiving a 404.