Unable to add kisak-mesa PPA following the command on Launchpad

I am trying to add the kisak-mesa PPA to my system. I usually add PPAs by following the instructions on Launchpad. For this PPA, the instructions look like this:

However, when I run sudo add-apt-repository ppa:kisak/kisak-mesa exactly as instructed, it says "The user named '~kisak' has no PPA named 'ubuntu/kisak-mesa'" but then proceeds to tell me there is a PPA named kisak-mesa, which is exactly what I requested in the command.

What am I doing wrong? How can I install this PPA? Why are the instructions on Launchpad not working? Why is add-apt-repository implicitly adding ubuntu/?

I'm using Ubuntu 20.04 LTS on x86_64.