For Widevine requests, we take the template as a string. We should be sending whatever information you provide in the template all the way through to the Google Widevine server.
I have not tested this flow myself, but when we get a Widevine request on the Key Delivery service, we just fill in details such as keyID, and sign it with our key. We don’t really do anything else other than that and send the request on to the license server hosted by Google for Widevine. We do not alter any part or the template in the actual license request.
The policyoverride object comes from the you as part of the WidevineConfiguration when creating ContentKeyPolicy. We do not set or alter the renewal_server_url that is set in there.
Are you sure that you have a valid template? If you can file an official support ticket with all the details on the account, and the template being used we can follow up.