postgresql-contrib-9.6 : Depends: libssl1.0.0 (>= 1.0.0) but it is not installable code example

Example: The following packages have unmet dependencies: nginx : Depends: libssl1.0.0 (>= 1.0.2~beta3)

echo "deb http://security.ubuntu.com/ubuntu bionic-security main" | sudo tee -a /etc/apt/sources.list.d/bionic.list
sudo apt update
apt-cache policy libssl1.0-dev
sudo apt-get install libssl1.0-dev