What is PHP Version 5?
The first stable version of PHP 5 is version 5.0.3 which was released in December 2004. The current PHP 5 version is 5.6.31 which was released in July 2017 and will remain supported until December 2018.
SubscriptionBoss requires at least PHP version 5.3 to operate correctly. And SubscriptionBoss also supports PHP 7 too
Is My Site Running PHP Version 5?
If you have you have been with your host less than 5 years or you are running on a shared server then you are almost certainly running PHP 5 already.
Your host provider should be able to tell you what version of PHP you are running on your server or you can check yourself. See How To Find What version of PHP my site is running?
How To Upgrade My Web Site to PHP 5
The easiest way to get this done is to ask your web site host to upgrade your site to PHP 5.
If you prefer to do this yourself the latest version of PHP can de downloaded at from the PHP Downloads page