What OS are you installing to?  I am installing on my private server in a VMware VM on esxi behind a natted cisco firewall.  The first scenario was on CENTOS 7 with the chat on the same system unit,  Virtualmin and Webmin were in place too.   I gave up on trying to work it into the UNA interface.  That said,  Rocket chat did work,  but I dont want to take the time to instruct you on how to fall short.    Let me know what you are working with and maybe I can help.   in the meantime,  this attempt that I am making now is on Debian 10 buster..