I am using elementary OS. When AppCenter is opened, a message is popped up with below message: does not have a Release file
E: The repository 'http://ppa.launchpad.net/versable/elementary-update/ubuntu bionic Release' does not have a Release file.
W: Updating from such a repository can't be done securely, and is therefore disabled by default.
W: See apt-secure(8) manpage for repository creation and user configuration details**
Also 'sudo apt-get update' gives result as:
Hit:7 http://ppa.launchpad.net/philip.scott/elementary-tweaks/ubuntu bionic InRelease
Ign:8 http://ppa.launchpad.net/versable/elementary-update/ubuntu bionic InRelease
Err:9 http://ppa.launchpad.net/versable/elementary-update/ubuntu bionic Release
404 Not Found [IP: 91.189.95.83 80] Reading package lists... Done E: The repository 'http://ppa.launchpad.net/versable/elementary-update/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.