Please copy & paste to your terminal:
sudo apt install lsb-release wget apt-transport-https bzip2
wget -qO- https://repo.vitexsoftware.com/keyring.gpg | sudo tee /etc/apt/trusted.gpg.d/vitexsoftware.gpg
echo "deb [signed-by=/etc/apt/trusted.gpg.d/vitexsoftware.gpg] https://repo.vitexsoftware.com $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/vitexsoftware.list
sudo apt update
sudo apt install package(s)