Nginx Startup

I'm new here and and have a problem.

I use Ubuntu as VM on my Freenas for Reverse Proxy. I get at Startup from Ubuntu Following error:

After entering following command "sudo service nginx status" I get this error log :

Failed to start A high performance web server and a reverse proxy server.

root@Proxy:~# service nginx configtest
* Testing nginx configuration [ OK ]
This is what my reverse proxy.conf looks like :

server {
listen 80;
server_name freenas.domain.de;
location / {
proxy_pass http://freenas.domain.de:80;
}
}
server {
listen 81;
server_name nextcloud.domain.de;
location / {
proxy_pass http://nextcloud.domain.de:81;
}
}
server {
listen 82;
server_name plex.domain.de;
location / {
proxy_pass http://plex.domain.de:82;
}
}
Here is the IP Adresses from the Services on My Freenas

Nextcloud : 192.168.178.63:8282 Freenas : 192.168.178.63 Plex : 192.168.178.22:32400

root@Proxy:~# sudo service nginx status
● nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Sat 2020-01-11 03:49:24 CET; 58min left
Docs: man:nginx(8)
Process: 732 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=1/FAILURE)

Jan 11 03:49:23 Proxy systemd[1]: Starting A high performance web server and a reverse proxy server...
Jan 11 03:49:24 Proxy nginx[732]: nginx: [emerg] host not found in upstream "freenas.domain.de" in /etc/nginx/sites-enabled/reverse-proxy.conf:5
Jan 11 03:49:24 Proxy nginx[732]: nginx: configuration file /etc/nginx/nginx.conf test failed
Jan 11 03:49:24 Proxy systemd[1]: nginx.service: Control process exited, code=exited status=1
Jan 11 03:49:24 Proxy systemd[1]: nginx.service: Failed with result 'exit-code'.
Jan 11 03:49:24 Proxy systemd[1]: Failed to start A high performance web server and a reverse proxy server.
Can anyone help me?