Issue - fastcgi_cache_purge

Hey everybody!

I have installed Nginx HDA Bundle from here https://launchpad.net/~hda-me/+archive/ubuntu/nginx-stable/+packages1 with some dynamic modules along ngx_cache_purge on Ubuntu 16.04.3 LTS (GNU/Linux 4.13.0-16-generic x86_64)

I'm using PHP 7.0.22-0ubuntu0.16.04.1 with nginx/1.13.6 and php7.0-fpm

I have loaded the ngx_cache_purge module in nginx.conf and added the following configuration to the vhost file:

location ~ /purge(/.*) {
fastcgi_cache_purge WPCACHE "$scheme$request_method$host$1";
return 200;
}

Code (markup):

For some reason when I try to purge the cache with

http://mydomain.com/purge/wordpress_post

Code (markup):

the browser attempts to download a file called "download" , 0bytes in size. I mention that the website is running with no errors and the cache files are created.

No errors in nginx.log nor php7.0-fpm.log.

What am I doing wrong here as I'm stuck on this situation for about one week and haven't found a solution yet. How can I debug this issue? Where should I look in order to find out what is the cause for this?