Hi there, the problem is solved. I contacted the host. Here is the reply:
In the root directory of your domain there are always 2 folders DE and EN in which an index.html is located, which generates this Checkdomain Parking page. You did not overwrite this data during the WordPress installation, if you activate the plugin, this will probably continue on /en. We have removed the old, no longer needed data – the process should now work.
Best regards,
Markus
