Install php5.6 on debian 10

1) update and install package

$ sudo apt update
$ sudo apt upgrade
$ sudo apt install ca-certificates apt-transport-https lsb-release
$ sudo apt install gnupg gnupg2 gnupg1
$ wget -q https://packages.sury.org/php/apt.gpg -O- | sudo apt-key add -
$ echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/php.list

2) Installation PHP5.6

$ sudo apt update
$ sudo apt install php5.6

Check install php5.6 completed

$ php -v