Webserver Nginx download the index file when I want to go to the first page

this is my Nginx config file

    ############# DOMAIN domainname.COM ####################
    server {
    server_name  domainname.com;
    rewrite ^(.*) http://www.domainname.com$1 permanent;
    return 301 $scheme://domainname.name$request_uri;
    }
    server {
    # Basic Domain
    server_name www.domainname.com;
    root /home/www/domainname;
    access_log  /var/log/nginx-domainname-access.log;
    error_log   /var/log/nginx-domainname-error.log;
    error_page 500 502 503 504 /500.html;
    client_max_body_size 4G;
    keepalive_timeout 10;
    # rewrite ^(.+)/index.html$ $1 permanent;
    ## REDIRECT domainname.com/index(.php) to domainname.com/
    if ($request_uri ~ ^(.*/)index(?:\.php)?$) {
    return 301 $1;
    }
    # OR USE :
    ## REDIRECT domainname.com/index(.html) to domainname.com/
    if ($request_uri ~ ^(.*/)index(?:\.html)?$) {
    return 301 $1;
    }
    ## REDIRECT domainname.com/index.html to domainname.com/index
    #if ($request_uri ~ ^(.+)\.html$) {
    #    return 301  $1;
    #}
    
    # To remove a slash at the end:
    rewrite ^/(.*)/$ /$1 permanent;
    
    #try_files $uri $uri/index.html =404;
    #try_files $uri $uri/ /index.php?q=$uri&$args;
    error_page 404 /404.html;

    location / {
    # URLs to attempt, including pretty ones.
    try_files   $uri $uri/ /index.php?$query_string;
    index index.html index.php index.py;
    autoindex on;
    }
    # Remove trailing slash to please routing system.
    if (!-d $request_filename) {
        rewrite     ^/(.+)/$ /$1 permanent;
    }
 # cache Media: images, icons, video, audio, HTC
  location ~* \.(jpg|jpeg|gif|png|ico|cur|gz|svg|svgz|mp4|ogg|ogv|webm|htc)$ {
  expires 30d;
  add_header Cache-Control "public";
  }
  # cache.appcache, your document html and data
  location ~* \.(manifest|appcache|html?|xml|json)$ {
  expires -1;
  # access_log logs/static.log; # I don't usually include a static log
  }
  location ~* \.(css|js)$ {
   expires 7d;
  }
  # Feed
  location ~* \.(rss|atom)$ {
  expires 1h;
  add_header Cache-Control "public";
  }                                                  
  }
  
server {
   server_name ~^(www\.)(?<subdomain>.+).domainname.com$ ;
   root /home/www/domainname/$subdomain;
}
server {
   server_name ~^(?<subdomain>.+).domainname.com$ ;
   root /home/www/domainname/$subdomain;
}

But Nginx download the index file when I want to go to the first page

then I want to know about “location /” code segment

and I want to know why this occurred

Meanwhile, I had a 403 Forbidden error message before

My used Os is WordPress

please see the code and write me the correct one

I installed WHMCS on a subfolder and I want to know about that

please edit the code to get access to my installed WHMCS on the subfolder too.

thanks ahead and much appreciated