For the Push Notification Bridge to connect to GCM, it must authenticate with an API key. You can get an API key from the Google Developers Console.

1. In the Google Developers Console, create or select a project.
   https://console.developers.google.com/home/
2. Go to Use Google APIs.
3. Select Cloud Messaging for Android.
4. Click Enable API.
   You are prompted to create credentials.
5. Choose to skip the step and create an API key.
6. In the Create a new key dialog, select Server key.
7. Type a name for the key.
   You can choose at this time to restrict the IP addresses that requests the use this API key can come from. If possible, restrict the key to the IP address your Push Notification Bridge uses.
8. Click OK.
   A dialog displays your new API key.