Does anyone have an example of how to form the body for the Lava WebRequest? I've been able to use Lava WebRequest for anything that doesn't require a body. I'm guessing it is a syntax issue, but I can't find an example of how to format the lava block. Keeping it simple, I'm trying right now just to login to the rocksolidchurchdemo site using the following lava block:

{% webrequest url: 'http://rock.rocksolidchurchdemo.com/api/Auth/Login' requestcontenttype:'application/json' responsecontenttype:'application/json' method:'POST' body: '{"Username" : "admin","Password" : "admin","Persisted" : "true"}' %}

{{result}}

{% endwebrequest %}

No matter how I try to form this, the constant result back is : Liquid error: The given key was not present in the dictionary. 

I've tried assigning a json variable to the body text using the FromJSON filter, but I get the same result.

Anyone point me in the right direction?  Any example of a webrequest with a body in it?