Unless you changed the location, then have a look in /var/log/nginx/error.log which will give you way more information on the problem. Just post the latest lines here if you don’t know what to do.

Thanks for the reply..I looked into the above file but didn’t find any error logs related to this website(fbclixs.com)..However, there are some error logs for other unrelated website(talkingsparrow.com) :

2017/02/23 11:12:53 [error] 31220#31220: *57434 FastCGI sent in stderr: “PHP message: PHP Notice: Use of undefined constant CURLOPTRETURNTRANSFER - assumed ‘CURLOPTRETURNTRANSFER’ in /var/www/talkingsparrow.com/html/wp-content/plugins/hueman-addons/assets/front/js/sharrre.php on line 38

Why this website is not logging any error, I couldn’t figure out.

I normally troubleshoot 500 errors by: checking .htaccess file, then checking RAM allocation on server, deactivating all plugins then turning them on 1 by 1, and then as a last resort I wipe and do a vanilla install of Wordpress to see if a basic setup works. Normally it’s .htaccess or RAM allocation, though.