Installer won't accept allowable hostnames e.g. hostname `123-abc`

[pelephant2]

System details

Omarchy v3.2.3

What's wrong?

The Omarchy v3.2.3 iso installer won't accept the hostname 123-abc and throws the error:

Hostname must be alphanumeric using dashes or underscores but no spaces

I get around this by accepting the default host name Omarchy and then later changing the hostname with sudo hostnamectl set-hostname <new-hostname>:

~ > hostname
omarchy

~ > sudo hostnamectl set-hostname 123-abc
~ > hostname
123-abc