Trying to send my docker logs without success

I have an app run on a docker container, the logs of the app are saved in /var/logs/app.log.
I’m trying to send the logs to a remote Syslog server.
I’m using this command:
$ docker run -d --log-driver syslog --log-opt syslog-address=‘udp://{host}:514’ --log-opt labels=‘label’ my_app

But when I checked the remote Syslog the logs not sent.
What do I need to change in order to send the logs to the remote Syslog?