Plesk supports multiple PHP versions. Different PHP versions are sometimes not fully compatible with the website written on another PHP version. For example, a website written in PHP 5.4 might not function properly if your domain is configured in PHP 5.6. If you are not sure which PHP version to choose, you can always configure it to the default setting, the latest or another version available on the system.
For you to choose the PHP version that will be compatible with your website. First, you need to Login to your Plesk account. (Don’t know how to login to your Plesk account? Click here)