I have problem with xfce4-gtk3
because when updating I get error
The repository 'http://ppa.launchpad.net/xubuntu-dev/xfce4-gtk3/ubuntu xenial Release' does not have a Release file.
Here is complete output of apt update
$ sudo apt update
Ign:1 http://linux.dropbox.com/ubuntu wily InRelease
Hit:3 http://linux.dropbox.com/ubuntu wily Release
Get:5 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB]
Hit:6 http://ppa.launchpad.net/linuxgndu/sqlitebrowser/ubuntu xenial InRelease
Hit:7 http://archive.ubuntu.com/ubuntu xenial InRelease
Get:8 http://archive.ubuntu.com/ubuntu xenial-updates InRelease [102 kB]
Hit:10 http://ppa.launchpad.net/mystic-mirage/pycharm/ubuntu xenial InRelease
Hit:11 https://deb.nodesource.com/node_6.x xenial InRelease
Hit:12 http://ppa.launchpad.net/nilarimogard/webupd8/ubuntu xenial InRelease
Hit:13 http://ppa.launchpad.net/numix/ppa/ubuntu xenial InRelease
Hit:14 http://ppa.launchpad.net/peek-developers/stable/ubuntu xenial InRelease
Hit:15 http://ppa.launchpad.net/ubuntu-desktop/ubuntu-make/ubuntu xenial InRelease
Get:16 http://archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB]
Hit:17 http://ppa.launchpad.net/webupd8team/sublime-text-3/ubuntu xenial InRelease
Ign:18 http://ppa.launchpad.net/xubuntu-dev/xfce4-gtk3/ubuntu xenial InRelease
Err:19 http://ppa.launchpad.net/xubuntu-dev/xfce4-gtk3/ubuntu xenial Release
403 Forbidden
Ign:20 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:21 http://dl.google.com/linux/chrome/deb stable Release
Hit:22 http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease
Hit:23 http://repository.spotify.com stable InRelease
Hit:2 http://screenshots.getdeb.net xenial-getdeb InRelease
Hit:4 http://screenshots.getdeb.net trusty-getdeb InRelease
Hit:25 https://packagecloud.io/slacktechnologies/slack/debian jessie InRelease
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/xubuntu-dev/xfce4-gtk3/ubuntu xenial 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.
Is the problem on my side or coming from xubuntu?