Upon closer examination, I found that not only do I have an /etc/kamailio/kamailio.cfg
file but /etc/kamailio/kamailio-advanced.cfg.
I made the changes the article suggested for kamailio.cfg in kamailio-advanced.cfg instead... and all is well. I was able to start the service again. I'm not sure if the database will work but at least I'm one step closer and now authentication is working.