Exceptions in HTTP(WSGI)+JsonDocument Spyne Client

Question

I've programmed a server-side service using Spyne. I want to use the Spyne client code, but I can't do it without having exceptions.

The server side code is something like (I've removed the imports and unified files):

class NotificationsRPC(ServiceBase):
    @rpc(Uuid, DateTime, _returns=Integer)
    def new_player(ctx, player_uuid, birthday):
        # A lot of irrelevant code
        return 0

    @rpc(Uuid, _returns=Integer)
    def deleted_player(ctx, player_uuid):
        # A lot of irrelevant code
        return 0

    # Many other similar methods

radiante_app = Application(
    [NotificationsRPC],
    tns="radiante.rpc",
    in_protocol=JsonDocument(validator="soft"),
    out_protocol=JsonDocument()
)
wsgi_app = WsgiApplication(radiante_app)
server = make_server('127.0.0.1', 27182, wsgi_app)
server.serve_forever()

This code runs properly, I can make requests to it through CURL (the real code is implemented using uWSGI, but in this example I'm using the python embedded WSGI server).

The problem appears in the client-side code. It's something like (RadianteRPC is the same class as in server-side, but with pass in the methods body:

radiante_app = Application(
    [RadianteRPC],
    tns="radiante.rpc",
    in_protocol=JsonDocument(validator="soft"),
    out_protocol=JsonDocument()
)
rad_client = HttpClient("http://127.0.0.1:27182", radiante_app)

# In the real code, the parameters have more sense.
rad_client.service.new_player(uuid.UUID(), datetime.utcnow())

Then, when the code is executed I have the following error:

File "/vagrant/apps/radsync/signal_hooks/player.py", line 74, in _player_post_save
created
File "/home/vagrant/devenv/local/lib/python2.7/site-packages/spyne/client/http.py", line 64, in __call__
self.get_in_object(self.ctx)
File "/home/vagrant/devenv/local/lib/python2.7/site-packages/spyne/client/_base.py", line 144, in get_in_object
message=self.app.in_protocol.RESPONSE)
File "/home/vagrant/devenv/local/lib/python2.7/site-packages/spyne/protocol/dictdoc.py", line 278, in decompose_incoming_envelope
raise ValidationError("Need a dictionary with exactly one key "
ValidationError: Fault(Client.ValidationError: 'The value "\'Need a dictionary with exactly one key as method name.\'" could not be validated.')

It's worth noting that the client is implemented in Django U_u (not my decision), but I think it hasn't relation with the problem.

I've followed some indications from this question (adapting the example of ZeroMQ transport protocol to HTTP transport protocol): There is an example of Spyne client?

Thank you for your attention.