There isn’t any mention of webhooks in the AxiDraw Merge manual, so I’m not sure what it is that you’re referring to there.
Webhooks may be added to AxiDraw Merge in a future release, but there is not currently any plan for a CLI version of AxiDraw Merge. In most cases, if you’re building automations, we would recommend to use the Hershey Advanced CLI (or the Python library), in combination with the AxiDraw CLI (or the Python library). *That* workflow does already exist and does support webhooks.