Forbiden to buy premium version

Hi Dear
I want to buy premium version of this plugin for my site.

But when i click on the download button to buy and activate it ,
i get this error in this link:
http://api.wpfastestcache.net/premium/newdownload/%5BHIDDEN%5D/c3381668ec080681935a2a3dd694e5b2
with content of :
Forbidden

Please help me to correctly download premium version.

thanks