How to write a server to send push messages using the django_push_notifications library?

Question

Django

Who can intelligibly explain the work of this library, otherwise I would have understood, but I feel that I am missing something.
I'm especially interested in working with registration_id and device_id. The service should work through GCM. Yeah, I registered an application there. And here's where I get stuck.
The server receives
url(r'^push/(?P[0-9]+)/$', push, name='push-message'), + POST
Function:
def push(request, **kwargs) :
devices = GCMDevice.objects.filter(user=kwargs['cid']).all()
message = request.POST.get("message_text") or 'Test message'
devices.send_message(message)
Server response:
HTTP Error 400: Bad Request

Answer 1

Let's abstract from the library and figure out where and what you are sending.
You need to send a POST request to https://gcm-http.googleapis.com/gcm/send
with a JSON array and your key in the header.
If you get 400, then you have, for example, the wrong key is being transmitted.