$ sudo apt-add-repository https:/dl.winehq.org/wine-builds/ubuntu/
[sudo] password for charles:
Ign:1 https:/dl.winehq.org/wine-builds/ubuntu bionic InRelease
Err:2 https:/dl.winehq.org/wine-builds/ubuntu bionic Release
  Undetermined Error
Get:3 https://dl.winehq.org/wine-builds/ubuntu bionic InRelease [4,701 B]
Hit:4 http://us.archive.ubuntu.com/ubuntu bionic InRelease
Err:3 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 818A435C5FCBF54A
Get:5 http://us.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Get:6 http://security.ubuntu.com/ubuntu bionic-security InRelease [83.2 kB]
Hit:7 http://archive.canonical.com bionic InRelease
Hit:8 http://ppa.launchpad.net/papirus/papirus/ubuntu bionic InRelease
Hit:9 https://download.sublimetext.com apt/stable/ InRelease
Get:10 http://us.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
Ign:11 https://download.opensuse.org/repositories/Emulators:/Wine:/Debian/Ubuntu_18.10_standard ./ InRelease
Hit:12 https://download.opensuse.org/repositories/Emulators:/Wine:/Debian/Ubuntu_18.10_standard ./ Release
Reading package lists... Done
E: The repository 'https:/dl.winehq.org/wine-builds/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.
W: 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 818A435C5FCBF54A
E: The repository 'https://dl.winehq.org/wine-builds/ubuntu bionic InRelease' is not signed.
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.