the output from the script shows the following:
INFO - Download of http://software.virtualmin.com/gpl/rhel/7.6.1810/x86_64/virtualmin-release-latest.noarch.rpm Succeeded.
error: open of <!DOCTYPE failed: No such file or directory
error: open of HTML failed: No such file or directory
...
the install log has the following in it:
INFO - 2019-04-04 11:20:36 - Started installation log in /root/virtualmin-install.log
DEBUG - 2019-04-04 11:20:36 - Install mode: full
DEBUG - 2019-04-04 11:20:36 - Product: Virtualmin GPL
DEBUG - 2019-04-04 11:20:36 - Virtualmin Meta-Package list: virtualmin-base
DEBUG - 2019-04-04 11:20:37 - install.sh version: 1.1.5
INFO - 2019-04-04 11:20:37 - Checking for fully qualified hostname…
INFO - 2019-04-04 11:20:37 - Hostname OK: fully qualified as *********
INFO - 2019-04-04 11:20:37 - Installing serial number and license key into /etc/virtualmin-license
INFO - 2019-04-04 11:20:37 - Loading OS selection library…
INFO - 2019-04-04 11:20:37 - Download of http://software.virtualmin.com/lib/oschooser.pl Succeeded.
INFO - 2019-04-04 11:20:37 - Loading OS list…
INFO - 2019-04-04 11:20:37 - Download of http://software.virtualmin.com/lib/os_list.txt Succeeded.
INFO - 2019-04-04 11:20:37 - Operating system name: CentOS Linux
INFO - 2019-04-04 11:20:37 - Operating system version: 7.6.1810
INFO - 2019-04-04 11:20:37 - Configuring package manager for CentOS Linux 7.6.1810…
INFO - 2019-04-04 11:20:37 - Disabling SELinux during installation…
DEBUG - 2019-04-04 11:20:37 - setenforce 0 succeeded
INFO - 2019-04-04 11:20:37 - Download of http://software.virtualmin.com/gpl/rhel/7.6.1810/x86_64/virtualmin-release-latest.noarch.rpm Succeeded.
FATAL - 2019-04-04 11:20:37 - Fatal Error Occurred: Installation of virtualmin-release failed: 22
FATAL - 2019-04-04 11:20:37 - Cannot continue installation.
FATAL - 2019-04-04 11:20:38 - Attempting to remove virtualmin repository configuration, so the installation can be
FATAL - 2019-04-04 11:20:38 - re-attempted after any problems have been resolved.
FATAL - 2019-04-04 11:20:38 - Removing temporary directory and files.
FATAL - 2019-04-04 11:20:38 - If you are unsure of what went wrong, you may wish to review the log
FATAL - 2019-04-04 11:20:38 - in /root/virtualmin-install.log