PHP5.6 on Debian 9
To have PHP5.6 available in Debian 9.
We really know it's possible to have it because in a Debian 9.0 machine we have it installed with a Little trick.
But using PLESK we are not able to install it.
The problem in that PHP5.6 is not compatible with Debian9 on the system level. Therefore we can’t release our PHP5.6 packages for this operating system. Please use PHP 7.x versions there.