diff --git a/sylk/applications/webrtcgateway/push.py b/sylk/applications/webrtcgateway/push.py
index c7cda48..a19be1a 100644
--- a/sylk/applications/webrtcgateway/push.py
+++ b/sylk/applications/webrtcgateway/push.py
@@ -1,80 +1,80 @@
 
 import json
 
 from twisted.internet import defer, reactor
 from twisted.web.client import Agent
 from twisted.web.iweb import IBodyProducer
 from twisted.web.http_headers import Headers
 from zope.interface import implementer
 
 from .configuration import GeneralConfig
 from .logger import log
 from .models import firebase
 from .storage import TokenStorage
 
 
 __all__ = 'incoming_call', 'missed_call', 'conference_invite'
 
 
 agent = Agent(reactor)
 headers = Headers({'User-Agent': ['SylkServer'],
                    'Content-Type': ['application/json'],
                    'Authorization': ['key=%s' % GeneralConfig.firebase_server_key]})
 FIREBASE_API_URL = 'https://fcm.googleapis.com/fcm/send'
 
 
 @implementer(IBodyProducer)
 class StringProducer(object):
     def __init__(self, data):
         self.body = data
         self.length = len(data)
 
     def startProducing(self, consumer):
         consumer.write(self.body)
         return defer.succeed(None)
 
     def pauseProducing(self):
         pass
 
     def stopProducing(self):
         pass
 
 
 def incoming_call(originator, destination):
     tokens = TokenStorage()
     request = firebase.FirebaseRequest(token='dummy', event=firebase.IncomingCallEvent(originator=originator, destination=destination), time_to_live=60)
     for token in tokens[destination]:
         request.to = token
         _send_push_notification(json.dumps(request.__data__))
 
 
 def missed_call(originator, destination):
     tokens = TokenStorage()
     request = firebase.FirebaseRequest(token='dummy', event=firebase.MissedCallEvent(originator=originator, destination=destination))
     for token in tokens[destination]:
         request.to = token
         _send_push_notification(json.dumps(request.__data__))
 
 
 def conference_invite(originator, destination, room):
     tokens = TokenStorage()
     request = firebase.FirebaseRequest(token='dummy', event=firebase.ConferenceInviteEvent(originator=originator, destination=destination, room=room), time_to_live=3600)
     for token in tokens[destination]:
         request.to = token
         _send_push_notification(json.dumps(request.__data__))
 
 
 @defer.inlineCallbacks
 def _send_push_notification(payload):
     if GeneralConfig.firebase_server_key:
         try:
             r = yield agent.request('POST', FIREBASE_API_URL, headers, StringProducer(payload))
         except Exception as e:
             log.info('Error sending Firebase message: %s', e)
         else:
             if r.code != 200:
-                log.warn('Error sending Firebase message: %s' % r.phrase)
+                log.warn('Error sending Firebase message: %s', r.phrase)
             else:
                 log.debug('Sent push notification: %s', payload)
     else:
         log.warn('Cannot send push notification: no Firebase server key configured')