This code system http://terminology.hl7.org/CodeSystem/endpoint-payload-type defines the following codes:

Code	Display	Definition
any	Any	Any payload type can be used with this endpoint, it is either a payload agnostic infrastructure (such as a storage repository), or some other type of endpoint where payload considerations are internally handled, and not available
none	None	This endpoint does not require any content to be sent; simply connecting to the endpoint is enough notification. This can be used as a 'ping' to wakeup a service to retrieve content, which could be to ensure security considerations are correctly handled