Hi,
Agama pro theme comes with bundled premium plugins so you get it at the price of the Agama Pro theme and do not have to pay extra for them, or for the subsequent registration and updates because we regularly update all plugins that come with the theme.
LayerSlider & Revolution Slider works properly without an activation code.
Only in the case, you want to access premium features, like importing demo sliders and unlock premium support, you will need to purchase a license.
Basically you Just need to create the Slider then enable it on your page from the Agama-options meta box.
http://docs.theme-vision.com/article/setup-a-revolution-slider/
The error you got, basically means that your hosting company is blocking some kind of requests to their servers (where your site is located).
So you will need to contact your hosting support team and ask for clarification. That will result in either certain security rule being disabled or (unlikely) the whole mod_security Apache module will be disabled for your site(s).
There are no other ways around and nothing can be done by the theme.
Regards