Ubuntu package repo unavailable

There seems to be something wrong with the apt repository. After adding:

deb http://downloads.skewed.de/apt/bionic bionic universe
deb-src http://downloads.skewed.de/apt/bionic bionic universe

to my apt lists and running sudo apt-get update, I get this error:

E: The repository 'http://downloads.skewed.de/apt/bionic bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.