No public key for during install

When going through the steps to install Jitsi on Ubuntu 18.04 I receive an error after adding the repository stable/.
“The repository ‘ stable/ InRelease’ is not signed.
Updating from such a repository can’t be done securely, and is therefore disabled by default.”

Can anyone point me in the right direction to fix this problem?

This is how to fix it
Execute the two commands one by one.

Thanks. I found my mistake. I was not putting sudo on my apt-key command. All is well now!