Hi Ben
When I try all sort of different things and absolutely nothing works, thats a pretty good sign that I am Mario Kart driving in the wrong direction on the grass. And I need to rethink my assumptions. I made a video of installing local_trigger, adding a webhook and testing it. Its about 5 mins all up. Lets hope this gets you back on the fast lane.
https://www.screencast.com/t/lkEDt9FlO7K
With regards support in Moodle. That is usually the domain of Moodle partners, or in some cases you might have an ad-hoc relationship with a Moodle professional. There are restrictions on who can promote themselves as able to provide Moodle services. Basically you need to have been approved by Moodle and stuff. I know there are Moodle partners who are flexible enough to allow you to host it in your own way, and just provide support.
I am from Poodll and we just support our own plugins. We do not provide Moodle services per se.
PS one other thing I did not add in the screencast, which could be pertinent. Moodle caches a lot of settings and stuff. After adding a webhook in local_trigger, you should 'purge all caches', to make sure Moodle picks it up. Do that at:
site admin->debugging->purge all caches