DLP Endpoint Flex Response Error

Hi,

I am new to Endpoint Flex Response and am trying to get my plugin to work. However, I am not even able to get the Flex Response example plugins to work and I can't find the error in the docs or logs.  On the incidents page in the admin console, the incident occurs, but the HelloWorld Flex rule gets the following error:

Flex Response Action Not Invoked

[HelloWorld] Plugin Host Not Available.

Anybody have any idea why this is happening and how to fix it?

Thanks!