Nginx cannot read the index file

Hello,
Nginx configuration is as follows:

server {
listen 80;
server_name default_server;
error_log /var/log/nginx/error.system-default.log;
access_log /var/log/nginx/access.system-default.log;
charset utf-8;

root /usr/share/nginx/html/;

location ~ \.php$ {
fastcgi_pass php-fpm:9000;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
add_header script-filename $document_root$fastcgi_script_name always;
include fastcgi_params;
}

location / {
try_files $uri =404;
index index.php index.html;
}
}

When I enter the IP address of the web server in the browser, I get a "404 Not Found" message and I must add the file name at the end of the IP address to display the index file. Which line is wrong?

Thank you.