If you have an application or hosting solution which was set up several years ago, there’s a reasonable chance that you are still running PHP 5. Security support for 5.6, the last version of PHP 5, ends on 31st December 2018, and after that date no more fixes will be released. The official recommendation is to upgrade to PHP 7 (there is no PHP 6), preferably 7.3 as this will be supported until December 2021.
Moving to the latest version of PHP 7 is likely to require changes to your web hosting platform and any applications you are running. In some cases the update is relatively painless and may even be automated, but if you are running a server which hasn’t been changed for several years or have a bespoke application the process may require more effort.
If you are in this situation, I am happy to continue supporting applications which require PHP 5 or help you migrate to PHP 7. I’ve helped different clients work with and upgrade from as far back as PHP 5.1, so I’m aware of the various problems that can crop up as part of the process.
If you would like help with supporting an old application, either on PHP 5 or to migrate to PHP 7, please feel free to contact me for a free initial discussion to start planning the way forward.