Ajax “POST” not working on HTTPS/SSL Nginx

I moved my magento store from non SSL to SSL (webserver: Nginx)

The problem : The site’s JS scripts ( Multiple Ajax function with “POST” ) has stopped working! Requests are fine but not able to get the response. Response headers (501 B)

I am very much sure this is due to Nginx webserver misconfiguration. Do i need to use reverse proxy to use SSL? If so how? Kindly advise.

My Nginx example.conf looks like this:

    server {
        listen      189.xx.xx.xx:80;
        server_name example.com;
        root        /home/example/public_html;
        index index.html index.php;
        return 301 https://example.com$request_uri;
    }

& My Nginx ssl-domain.conf looks like this:

server
    {
    listen      189.xx.xx.xx:443 default ssl;
    server_name example.com;
    root        /home/example/public_html;
    index index.html index.php;    
	
    ssl on;
    ssl_certificate /etc/ssl/example.crt;
    ssl_certificate_key /etc/ssl/example.key;
    ssl_prefer_server_ciphers on;
	
    location / {
        try_files $uri $uri/ /index.php;
        expires 30d;   
    }
	
  location ~* \.(gif|jpg|jpeg|pdf|txt|css|js|png|ico|xml|xml|gz)$ {
access_log  off;
	expires 30d;
	add_header Pragma public;
    add_header Cache-Control "public";
}

    location ~ \.php$ {
        expires off;
        fastcgi_read_timeout 900s;
        fastcgi_index index.php;
        fastcgi_pass 127.0.0.1:9000;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include /etc/nginx/conf/fastcgi_params;
    }

}