Domain Alias leads to the Plesk default page instead of the working directory

[netsetter]

Hello all,

as every stupid server administrator, I was expecting that when I add a domain alias (myaliasdomain.com) to the main domain (mymaindomain.com) with the http 301 redirect off, it would lead me to the right working folder,

/var/www/vhosts/mymaindomain.com/httpdocs/

but instead, when visiting http://myaliasdomain.com I just see the plesk default page in the .skel directory

Is this supposed to be like this? I am moving to a new server and my plan was to test if everything is alright by testing it with one of my other domains as an domain alias for the main domain.
Any idea what to change, so my alias domain will point to the right directory of the main domain?

Best regards