I haven't been able to track down any information on my own about this, so no one must be having an issue.
I tried to create a dispatch rule to take a ticket with a subject starting with CHN and launch a webhook POST to create a change request.
The webhook doesn't appear to run at all, I can set any other number of options to modify the ticket and everything works, just not anything as a webhook.
I have created a POST using the link below
I have tried the following
* No authentication, API Auth, User Auth
* Different trigger options (Sender, Subject)
* Changed rule to set a different custom field (source) and a Supervisor Rule to generate the Change