services.nginx = {
   enable = true;

   commonHttpConfig = ''
         # optimisation
        sendfile on;
        tcp_nopush on;
        tcp_nodelay on;
        keepalive_timeout 600;
        types_hash_max_size 4096;
        include ${recommendedProxyConfig};
   '';

error: undefined variable 'recommendedProxyConfig' at /etc/nixos/nextcloud.nix:23:19