See this post
Essentially you need to have a "/endpoint" prefix to the web hooks so your POST command looks something similar to
http://192.168.x.xx:1880/endpoint/hubitat/webhook
In Mrobi's case he also had a password on his NR instance, so he was getting authentication error in his logs. He simply added the "username:pass@ip" format to the url...AND also had to remove special characters from his password.
I personally don't put a pass on my NR instance since it is not exposed to the web and just creates extra headaches with integrations.
