ttp://ppa.launchpad.net/leolik/leolik/ubuntu bionic Release code example

Example: Err:15 http://ppa.launchpad.net/gnome-terminator/ppa/ubuntu bionic Release 404 Not Found [IP: 91.189.95.83 80]

1. Open Software & Updates, Other Software tab.
2. find the PPA definition that contains "gnome-terminator"
3. select it and click Edit
4. change the Distribution field from bionic to xenial
5. save the changes
6. update the software database when prompted
problem solved