Reverse proxy nginx 502 bad gateway

I’ve been looking for a solution to my problem for two days but unfortunately I can not find the solution anywhere I hope you can help me.
I am still a beginner please be nice :smiley:

I am using unraid and the NRP and Vaultwarden are running on a docker.
The NRP works I can reach rocketchat without problems but it won’t work on Vaultwarden.
these are my settings:
(unfortunately I can only upload one picture so it does not look so nice)

Advanced:

location /admin {
  return 404;
  }

  location / {
    proxy_pass http://192.168.2.13:4743;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
  }
  
  location /notifications/hub {
    proxy_pass http://192.168.2.13:3012;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
  }
  
  location /notifications/hub/negotiate {
    proxy_pass http://192.168.2.13:4743;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
  }

thank you for your help !!!