Install PHP 5.6 on Debian
Debian 9 come with PHP 7. To install PHP 5.6, run
apt install apt-transport-https lsb-release ca-certificates -y wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg sh -c 'echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list' apt-get update
Install PHP 5.6 with
apt install -y php5.6 php5.6-mysql php5.6-gd php5.6-mbstring php5.6-mcrypt php5.6-zip php5.6-curl php5.6-xml
Enable SimpleXML module
phpenmod -v 5.6 simplexml
Install php-fpm if required
apt install -y php5.6-fpm
See php