Configuration for NGINX for subfolder

[hgue]

Hi,
I try to use the dashboard on a subfolder within my current nginx configuration.
Somehow I cannot get it to work with the location '/admin' as a subfolder path. All other endpoints are working well.
Can anyone help me here? I am not using traefik, so this setup is not helpful for me as explained in the docs.

Here is my current nginx setup:

server {
  listen 443 ssl;
  listen [::]:443 ssl; 
  # For the federation port
  listen 8448 ssl default_server;
  listen [::]:8448 ssl default_server;

  http2 on;
  server_name matrix.example.com;

  ### SSL
  include inc/default_ssl.conf;
  include inc/default_ssl_example.com.conf;

  ### Logging
  access_log /var/log/nginx/matrix.example.com.log;
  error_log /var/log/nginx/matrix.example.com.log;

  ### Nginx
  server_tokens off;
  chunked_transfer_encoding off;

  ### Locations / Routing

  include inc/error_pages.conf;

  location /admin {
    rewrite ^/admin(.*) $1 break;      
    proxy_pass http://10.1.0.36/;
    
    index index.html;
    try_files $uri $uri/ /admin/index.html;

    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection 'upgrade';

    include inc/default_proxy_params.conf; 
  }

  location ~* ^(\/_matrix|\/_synapse\/client) {
    proxy_pass http://10.1.0.30:8008;

    # Nginx by default only allows file uploads up to 1M in size
    # Increase client_max_body_size to match max_upload_size defined in homeserver.yaml
    client_max_body_size 50M;
    
    include inc/default_proxy_params.conf;
  }

  location ~ ^/(client/|_matrix/client/unstable/org.matrix.msc3575/sync) {
    proxy_pass http://10.1.0.35:8009;

    include inc/default_proxy_params.conf;
  }

  location /.well-known/matrix/server {
    # Allow access from *
    add_header Access-Control-Allow-Origin '*';
    default_type application/json;
    return 200 '{ "m.server": "matrix.example.com:443" }';
  }

  location /.well-known/matrix/client {
    # Allow access from *
    add_header Access-Control-Allow-Origin '*';
    default_type application/json;
    return 200 '{ "m.homeserver": { "base_url": "https://matrix.example.com" }, "m.identity_server": { "base_url": "https://vector.im" }, "org.matrix.msc3575.proxy": { "url": "https://matrix.example.com" } }';
  }

  # Element.io client
  location / {
    # note: do not add a path (even a single /) after the port in `proxy_pass`,
    # otherwise nginx will canonicalise the URI and cause signature verification
    # errors.
    proxy_pass http://10.1.0.33:80; # container_ip from network for element chat
    # Nginx by default only allows file uploads up to 1M in size
    # Increase client_max_body_size to match max_upload_size defined in homeserver.yaml
    client_max_body_size 50M;

    # Content Security Policy (see https://forum.seafile.com/t/content-security-policy/4071)
    add_header "Content-Security-Policy" "default-src 'self'; script-src * 'unsafe-eval' 'wasm-unsafe-eval'; font-src 'self' data:; style-src 'self' 'unsafe-inline' fonts.googleapis.com; child-src * blob: data:; media-src * blob: data:; object-src 'none'; img-src * data: blob:; connect-src * blob:; worker-src * blob:; frame-src * blob: data:";
    # HTTP Strict Transport Security (HSTS)
    add_header Strict-Transport-Security "max-age=31536000; includeSubDomains;" always; 

    include inc/default_proxy_params.conf;
  }

}