Try "apt-mark showhold" and then "apt-mark unhold package-name". Or try to "purge" and "autoremove" and reinstall after it. If that fails, try it with "aptitude".
And I am not sure, but I read something about not using the autoinstaller. But that might be fixed or misunderstood.
Oder einfach wie in dem Zitat, der Fix kommt direkt von Nuxwin und funktioniert zu 100%.
Whats inside the htdocs folder?
How does the vhost look like?
Either you wait or you downgrade. The update for Buster might take some time.
If its a productive system, I would downgrade (or backup and reinstall).
Mind if you share the changes so others might benefit from it? 
Check this post: Abwesenheitsbenachrichtigung keine Umlaute
It explains what to do. You dont need to restart a service.
Check that.
Ah, yes. I see.^^
I forgot that its about the experimental version. 
Because 7.2 isnt supported. 
7.0 should be supported too, at least via the php Switcher.
Keep in mind please, its an unstable version. Means it shouldnt be used in a productive (live) environment.
That what you posted as the vhost file, isnt actually the vhost file.
Do you use any plugins for i-MSCP?
Is the i-MSCP version up to date?
Is there a .htaccess file in that directory? Keep in mind, that you need to search especially for hidden files.
Try to delete the file and upload a new index.php or index.html. Use the following content:
Did you change something manually?Is that a new installation?
Try "/var/www/imscp/engine/setup/imscp-reconfigure -r httpd" . If that doesnt solve it, you might try "/var/www/imscp/engine/setup/imscp-reconfigure -r all".
If you do that commands, make sure to disable any used plugins before you do it (better safe than sorry).
What joximu posted is actually a very good idea. Why didnt I thought about checking the access and error logs from that domain? 
