WordPress Chat Ajax not showing up?

Hello guys!!!

I have a BuddyPress+WPMU live project and I want to use this chat plugin. In my test site in WPEngine I activate the plugin and I can go to site settings>>Setting Common and I can see two types of Ajax: Plugin Ajax and WordPress Ajax.

But when I go to my project server that is not on WPEngine is a dedicated server, I see just WordPress Ajax… And when I activate the plugin my server goes down and I get this error:

Error 503 Service Unavailable

Service Unavailable

Guru Meditation:

XID: 1521634984

Varnish cache server

What do I have to do to use this plugin?