You have to add your domain to the developers console.
How to:
- Log in to the Google Developers Console
- Select your project
- Under ‘APIS & AUTH’ select ‘Push’
- Click ‘Add domains’
- Enter the needed domains (Only the domain is needed, not the whole notification url)
- Click the ‘Add domains’ button
After that it should work unless there’s something else wrong with what you’re doing :p