wget -O - https://wapt.tranquil.it/debian/tiswapt-pub.gpg  | apt-key add -
echo  "deb  https://wapt.tranquil.it/debian/wapt-1.6/ $(lsb_release -c -s) main"  > /etc/apt/sources.list.d/wapt.list
=> deb https://wapt.tranquil.it/debian/wapt-1.6/ xenial main

apt update
=> Ign:6 https://wapt.tranquil.it/debian/wapt-1.6 xenial InRelease
=> Err:7 https://wapt.tranquil.it/debian/wapt-1.6 xenial Release
=>   404 Not Found