The object delivered to a webhook is a notification. Notifications have payloads, which contain the API’s existing JSON objects, such as the user.
The notification object consists of information about the API object type, method, and actual object.

Bulk notification object
A notification object will always be an array of notifications inside a bulk object read more about bulk object.

Name	Type	Definition
item_type	String	Describe the API item type.
topic	String	Describe the notification topic type. read more at supported topics
item	Hash	The issued item.

{
	"item_type":(String),
	"topic":(String),
	"item":{
  	...
	}             
}