Error while Installing Debian on a KVM --> apt configuration problem

currently I'm trying to install Debian 10 (newest version) on my freshly rested VM. I'm getting no errors, until the installer tries to Configure the package manager. Then I get the error, that "the attempt to configure apt to install additional packages from the CD failed." When I ignore that, and enter my mirror country and so, when the installer is trying to configure apt, it says that there's a "Bad archive mirror". So, what can I do? Any Ideas? I'm happy about everything :)