Cannot install network-manager-l2tp on Ubuntu18.04

Question

Trying to install network-manager-l2tp on Ubuntu 18.04.

sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp
sudo apt-get update
sudo apt-get install network-manager-l2tp-gnome

After this command

sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp

I am getting this:

    ...    
    E: The repository 'http://ppa.launchpad.net/nm-l2tp/network-manager-l2tp/ubuntu 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.
    E: The repository 'http://ppa.launchpad.net/seriy-pr/network-manager-l2tp/ubuntu 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.

How can I resolve this issue?

Answer 1

As we discovered during conversation with @Jos in comments:

the mentioned PPA (ppa:ubuntu/network-manager-l2tp) is not needed for Ubuntu 18.04 LTS.

If you have added it - remove it with:

sudo ppa-purge ppa:ubuntu/network-manager-l2tp

All packages are available in the universe repository (see link for network-manager-l2tp and link for libreswan).

So all you need is to enable universe repository and install packages from it:

sudo add-apt-repository universe
sudo apt-get update
sudo apt-get install network-manager-l2tp-gnome