Repositories errors

m@m-desktop:~$ sudo apt-add-repository ppa:qucs/qucs
[sudo] password for m:
This is the release PPA for qucs ubuntu packages, until qucs will be included in the official repository
More info: https://launchpad.net/~qucs/+archive/ubuntu/qucs
Press [ENTER] to continue or Ctrl-c to cancel adding it.

Hit:1 https://deb.opera.com/opera-stable stable InRelease
Get:2 https://dl.winehq.org/wine-builds/ubuntu bionic InRelease [6.257 B]
Hit:3 http://linux.teamviewer.com/deb stable InRelease
Err:2 https://dl.winehq.org/wine-builds/ubuntu bionic InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 76F1A20FF987672F
Hit:4 http://ar.archive.ubuntu.com/ubuntu bionic InRelease
Hit:5 http://archive.canonical.com/ubuntu bionic InRelease
Ign:6 http://ppa.launchpad.net/qucs/qucs/ubuntu bionic InRelease
Hit:7 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:8 http://ar.archive.ubuntu.com/ubuntu bionic-updates InRelease
Hit:9 http://ar.archive.ubuntu.com/ubuntu bionic-backports InRelease
Err:10 http://ppa.launchpad.net/qucs/qucs/ubuntu bionic Release
404 Not Found [IP: 91.189.95.83 80]
Reading package lists... Done
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://dl.winehq.org/wine-builds/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 76F1A20FF987672F
E: The repository 'http://ppa.launchpad.net/qucs/qucs/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.
m@m-desktop:~$