Cannot send docker container logs to graylog 3.3 with "gelf" driver

Hello,
I am a beginner in Graylog and I choose it to monitor docker container logs using gelf logging driver. To do that I created a gelf UDP input in Graylog web interface and I mentioned gelf as a log driver inside my docker-compose file. After starting the gelf udp input any log messege is sent from the container to Graylog input, so can you explain to me how can I fix this issue. Below my setup environment :

OS : debian 10
Docker version : 20.10.3
Graylog compose file : Docker — Graylog 3.3.8 documentation
My container compose file :

    ...
    logging: 
       driver: "gelf"
       options: 
            gelf-address: "udp://graylog:12201"
            tag: myContainer

Input:

NB: My container is running behind nginx reverse proxy.

Regards!