Uptime Kuma reverse proxy nginx config for a URL prefix

uptime-kuma.conf

# nginx configuration snippet for running Uptime Kuma on a URL prefix
# set up for yourdomain.com/kuma, with traffic forwarded to a docker 
# container with the hostname 'uptime-kuma'

  # Use docker's DNS
  resolver 127.0.0.11;  
  
  # uptime kuma
  location /uptime {

    # Define upstream address
    set $upstream_app uptime-kuma;
    set $url_prefix uptime;
    proxy_pass http://$upstream_app:3001;

    # Set proxy headers
    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;
    proxy_set_header X-Forwarded-Protocol $scheme;
    proxy_set_header X-Forwarded-Host $http_host;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_buffering off;

    # Redirect location headers
    proxy_redirect ^ /$url_prefix;
    proxy_redirect /dashboard /$url_prefix/dashboard;

    # Remove URL prefix to pass to the app
    rewrite ^/uptime/?(.*)$ /$1 break;

    # Sub filters to replace hardcoded paths
    proxy_set_header Accept-Encoding "";
    sub_filter_once off;
    sub_filter_types *;
    sub_filter '/assets/' '/$url_prefix/assets/';
    sub_filter '"assets/' '"$url_prefix/assets/';
    sub_filter '/dashboard' '/$url_prefix/dashboard';
    sub_filter '"/socket.io"' '"/$url_prefix/socket.io"';

    sub_filter '"/icon.svg"' '"/$url_prefix/icon.svg"';
    sub_filter '"/favicon.ico"' '"/$url_prefix/favicon.ico"';
    sub_filter '"/manifest.json"' '"/$url_prefix/manifest.json"';
  }

Thank you!
My nginx is not configured with --with-http_sub_module, so this is for anyone else who has encountered this problem:

Install libnginx-mod-http-subs-filter and make sure it's enabled in nginx config.

apt install libnginx-mod-http-subs-filter

And remove sub_filer_once off and change sub_ to subs_ in config.

    # Sub filters to replace hardcoded paths
    proxy_set_header Accept-Encoding "";
    subs_filter_types *;
    subs_filter '/assets/' '/$url_prefix/assets/';
    subs_filter '"assets/' '"$url_prefix/assets/';
    subs_filter '/dashboard' '/$url_prefix/dashboard';
    subs_filter '"/socket.io"' '"/$url_prefix/socket.io"';

    subs_filter '"/icon.svg"' '"/$url_prefix/icon.svg"';
    subs_filter '"/favicon.ico"' '"/$url_prefix/favicon.ico"';
    subs_filter '"/manifest.json"' '"/$url_prefix/manifest.json"';