ah i see.
it seems the site doesnt work when ure on
https://www.anteup.at/
but it does work when youre on
https://anteup.at/
i did code lay theme in a way where both urls should work but for some reason in your case it doesnt work. maybe there is a misconfiguration with how links are created in your wordpress installation.
my webhost gives me the option to only show websites with https:// instead of https://www
can you see if you have any options for your domain settings for this?
and then set the domain to only use https:// instead of https://www