How to successfully “Generate a Notification Key on the Client”?

[pushbit]

I'm following the below instructions, but the response is always HTTP 401 Unauthorized. I have verified that the ID token, registration ID, and project ID (number) are all valid. Unfortunately the response does not provide a detailed reason.

https://developer.android.com/google/gcm/notifications.html#gen-client

What is necessary to receive an HTTP 200 response with the notification_key? I'm wondering if the documentation is missing an important detail or if there is a known issue with the service. Otherwise GCM and the Google auth token are working fine for me.  It seems that the id_token field is not being used by the service. If I remove any other field, the response is {"error":"Missing \"{field-name}\" field"}. But it doesn't return a similar response when id_token is missing.

Here is a redacted net log. Does the request require any other headers or JSON fields that are not specified in the documentation?

---> HTTP POST https://android.googleapis.com/gcm/googlenotification

project_id: {project-number}

Content-Type: application/json; charset=UTF-8

{"id_token":"{long-auth-token}",

"notification_key_name":"{unique-name}",

"operation":"add",

"registration_ids":["{reg-id}"]}

<--- HTTP 401 https://android.googleapis.com/gcm/googlenotification