When I add the proxy_bind parameter, requests are never forwarded to the server behind. If I do not add it, the output on the turn server is as follows.

Output:
96: handle_udp_packet: New UDP endpoint: local addr Turn_Server_IP:3478, remote addr NGINX_IP:59902

stream {

upstream stream_backend {
server Turn_Server_IP:3478;
}

server {
listen 3478 udp;
proxy_pass stream_backend;
proxy_bind $remote_addr transparent;
}

}

Thanks for help.