code: def sign(self, payload):
          
          nonce = str(int(time.time() * 1000))
          package = {'apikey': self.key,
                     'message': {'nonce': nonce, 'payload': payload}}
  
          signature = hmac.new(self.secret, json.dumps(payload).hexdigest,
                               hashlib.sha512).hexdigest()
          package['signature'] = signature
  
          return json.dumps(package)
docs: Signature method which wraps signature and nonce parameters around a
          payload dictionary.
          :param payload:
          :return: