how to use Observer

[EricLjr]

class TestConsumer(ObserverModelInstanceMixin, GenericAsyncAPIConsumer):
queryset = get_user_model().objects.all()
serializer_class = UserSerializer

When I subscribed to the model, I found that using the code in the example, the action subscribe_instance does not take effect, but the Retrieve is OK
Could you please tell me the details of use
thank you very much!