It seems something is strange in their template.
I notice you are using Contabo, which I ranted about in another thread yesterday.
You should ideally scratch this server and start again. Use a newer OS for starters, CentOS 7 is old, and install Virtualmin yourself. It’s basically copy&paste from the Virtualmin install page.
This will give you a better starting point than a provider template that seems poorly configured since not even hostname is properly set.
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