I was trying to install kamailio for the first time but I could not activate it. I follow the steps of this installation https://powerpbx.org/content/kazoo-v4-single-server-install-guide-v1#detaile... The error given was  "Active: failed (Result: exit-code= since Mon 2021-03-08 15:44:55 (code=exited, status=255)"
The work around I found to solve this was to modify this archive vi /etc/kazoo/kamailio/local.cfg More precisely you need to uncomment some lines and verify the information is right and similar to the one I post here. In my case the hostname is ServerTest, the IP Address is 192.168.0.123.
################################################################################ ## SERVER INFORMATION ################################################################################ ## UNCOMMENT & CHANGE "somedomain.local" TO YOUR SERVERS HOSTNAME **#!substdef "!MY_HOSTNAME!ServerTest.local!g"**
## UNCOMMENT & CHANGE "192.168.88.51" TO YOUR SERVERS IP ADDRESS ## Usually your public IP. If you need ## to listen on addtional ports or IPs ## add them in "BINDINGS" at the bottom. **#!substdef "!MY_IP_ADDRESS!192.168.0.123!g"**
## CHANGE "kazoo://guest:guest@192.168.88.51:5672" TO THE AMQP URL ## This should be the primary RabbitMQ server ## in the zone that this server will service. **#!substdef "!MY_AMQP_URL!amqp://guest:guest@192.168.88.51:5672!g"**