It is documented at the beginning of the installation documentation in the prerequirement "(a) choose a domain (b) setup HTTPS for the domain". OTOH nobody ever reads documentations.
@tobias Thanks. Twice now the same guy has had the same problem in IRC, so there is definitely some user error.
It is pretty standard these days to set up TLS first, then install. But for yhe new sysadmin, it should be fixable without knowing SQL. That's my opinion.