"sudo apt-key add -" has no effect

Question

This command:

sudo add-apt-repository ppa:upubuntu-com/network -y

returns:

Cannot add PPA: ''This PPA does not support focal''.

Then I'll jump straight to the point by skipping the elementary part of "add-apt-repository" answered and over-answered.

This command:

sudo gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv A5D712AEE06E6293
sudo gpg -a --export A5D712AEE06E6293 | sudo apt-key add -
sudo bash -c "echo -e 'deb http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main\ndeb-src http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main' > /etc/apt/sources.list.d/upubuntu-com-ubuntu-network-wily.list"

returns the right output but then when I go to run:

sudo apt-get update

returns equally the error:

W: GPG error: http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily Release: The following signatures were invalid: DED04C8CBB517AE45B073F12A5D712AEE06E6293
E: The repository 'http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily Release' 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.

---------------------------------------- Update ----------------------------------------

The repositories:

deb [ trusted=yes allow-insecure=yes allow-weak=yes allow-downgrade-to-insecure=yes check-valid-until=no ] http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main
deb-src [ trusted=yes allow-insecure=yes allow-weak=yes allow-downgrade-to-insecure=yes check-valid-until=no ] http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main

With the command:

sudo apt-get update --allow-unauthenticated --allow-insecure-repositories

doesn't have effect but the error message becomes shorter:

W: GPG error: http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily Release: The following signatures were invalid: DED04C8CBB517AE45B073F12A5D712AEE06E6293

Answer 1

The PPA in question is outdated, its most recent supported Ubuntu release was “wily” (15.10). You should not use such a PPA on any currently supported Ubuntu version.

See also: What can I do if a repository/PPA does not have a Release file?, especially the answer by N0rbert might help you.

Answer 2

I looked at the problem from another perspective.

In the first case:

deb http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main
deb-src http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main

The command:

sudo apt-get update > /dev/null
echo $?

Returns the error code 100

In the second case:
deb [trusted=yes] http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main
deb-src [trusted=yes] http://ppa.launchpad.net/upubuntu-com/network/ubuntu wily main

for my surprise, the command:

sudo apt-get update > /dev/null
echo $?

Give me 0 code. Then I have suspected and tried

sudo apt-get install ipscan

And command does work!