nginx php7.0 fastcgi return internal server error on path

Question

I am configuring php7.0 fpm on nginx 1.10 on ububtu 16.04 server. After follwing thousands of instructions from web, I am still not able to get it to work.

I keep on getting internal server error in the browser with no error log whatsoever, neither in /var/log/nginx/error.log or /var/log/php7.0-fpm.log.

Even it is not logged in access.logs in nginx.

Here are my sites-available/default complete server block

# Default server configuration
#
server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html;

    # Add index.php to the list if you are using PHP
    index test.php index.html index.htm index.nginx-debian.html;

    server_name tasks.siteflu.com;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
    }

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    location ~ \.php$ {
        include snippets/fastcgi-php.conf;

        # With php7.0-cgi alone:
    #   fastcgi_pass 127.0.0.1:9000;
        # With php7.0-fpm:
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
    }

    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    location ~ /\.ht {
        deny all;
    }
}

I have tried almost all the resources available on the web and still cannot get it to work.

Also, if I specify a php file, say test.php, as index, it executes when the open mydomain.com.

But for the same file as mydomain.com/test.php, I get an Internal server error with no logging.