How to config coturn on Nginx for webRTC?

Question

I am making a WebRTC application which is working fine on wifi. But when I open the app on my phone via 4G the webRTC livestream wont start.

enter image description here

It seems something is going wrong by making the iceConnectionState. For the Iceserver I made a turn server with coturn on my Nginx server with the following settings:

listening-port=3478
tls-listening-port=5349
listening-ip=my-public-ip
relay-ip=my-public-ip
external-ip=my-public-ip
fingerprint
user=Dominique:GS7Yq_jK
lt-cred-mech
server-name=domain.com
realm=domain.com
log-file=/var/log/turnserver/turnserver.log
simple-log
external-ip=my-public-ip
total-quota=100
stale-nonce=600
Authentication method
use-auth-secret
static-auth-secret=33515e71ba1d0a96e77083f7e4215d99afe36204b6f382e1715fbb9314ae61d0
cert=/etc/letsencrypt/live/domain.com/fullchain.pem
pkey=/etc/letsencrypt/live/domain.com/privkey.pem

in my nginx.conf I added the following block

stream {
        server {
                listen 3478 udp;
                proxy_pass domain.com:3478;
        }
    server {
            listen 5349 udp;
            proxy_pass domain.com:5349;
    }

}

When I test my Turn server via this testing site

I get this result with these settings

 urls: 'turn:domain.com:3478',
  username: 'Dominique',
  credential: 'GS7Yq_jK'

enter image description here

is there anyone who can help me? I would like to get webRTC working on 4G

THanks for the help!

Gr, Dominique