However, step 4 just takes me to a 404 error page and it appears the callback portion of the URL references a private IP (which is the IP the LibreNMS server is). Not sure if this is the problem.
I also have the same problem. PagerDuty says that callback needs to be our PagerDuty integration name, not the one in the URL. There should be an additional input to put the integration name.
So, I actually got this integration to work. I didn’t even bother with the authorize button. What I did was create a new Service within PagerDuty and tied it to the LibreNMS service (by searching for it within PagerDuty while creating a new service). I copied the integration key the service generated in PagerDuty and placed it in the alert transport in LibreNMS.
Not even sure what the point of the authorize button is if I can get this to work using only the integration key. Also, seems that the documentation steps on both the LibreNMS and PagerDuty side (for the PagerDuty integration) are not listed out correctly.