Nginx fails to redirect '/' to '/index.php'

Nginx fails to call index.php file at ‘/’ endpoint. In /etc/nginx/sites-available/default, I have added location / section to rewrite to ‘/index.php’ (see below). However, when I enter my-site.com to the url bar, I get 403 Forbidden error ([error] 18041#18041: *2 directory index of “/var/www/html/” is forbidden).

When I enter my-site.com/index.php, it works correctly. Also, I’m able to see a page other than 403 Forbidden if I add an ‘index.html’ fie to my document directory, /var/www/html. Even with fastcgi_index index.php; and removed ‘index.html’, I don’t see the index.php file in ‘/’ endpoint.

/etc/nginx/sites-available/default

server {
	listen 80;
	listen [::]:80;
	server_name my-site.com www.my-site.com;
	return 301 https://$server_name$request_url;
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    
    include snippets/ssl-my-site.com.conf;
    include snippets/ssl-params.conf;

    root /var/www/html;

    index index.php index.html index.htm index.nginx-debian.html;

    server_name my-site.com www.my-site.com;

    location ~ [^/].php(/|$) {
        fastcgi_split_path_info ^(.+?.php)(/.*)$;
        
        if (!-f /var/www/html$fastcgi_script_name) {
            return 404;
        }
    
        include fastcgi_params;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME /var/www/html$fastcgi_script_name;
        fastcgi_pass unix:var/run/php/php7.0-fpm.sock;
        #fastcgi_pass  127.0.0.1:9000;
        fastcgi_read_timeout 300;
    }

    location ~ /.ht {
        deny all;
    }
    
    location ~ /.well-known {
        allow all;
    }

   location /phpmyadmin {
                index index.php;
    }

    # Rewrite rules for WordPress Multi-site.
    if (!-e $request_filename) {
            rewrite /wp-admin$ $scheme://$host$uri/ permanent;
            rewrite ^/[_0-9a-zA-Z-]+(/wp-.*) $1 last;
            rewrite ^/[_0-9a-zA-Z-]+(/.*\.php)$ $1 last;
    }
}