N.B.: All commands are supposed to be run by root. If you are logged in as a regular user with sudo rights, please prepend ___sudo___ to each of the commands.
During the installation, you will be asked to enter the hostname of the Jitsi Meet instance. If you have a FQDN hostname for the instance already set up in DNS, enter it there. If you don't have a resolvable hostname, you can enter the IP address of the machine (if it is static or doesn't change).
This hostname (or IP address) will be used for virtualhost configuration inside the Jitsi Meet and also, you and your correspondents will be using it to access the web conferences.
Launch again a browser with the Jitsi Meet URL and you'll see a telephone icon on the right end of the toolbar. Use it to invite SIP accounts to join the current conference.
The reason for failure is that sometimes, the uninstall script is faster than the process that stops the daemons. The second run of the uninstall command fixes this, as by then the jigasi or jvb daemons are already stopped.