This package is abandoned and no longer maintained. The author suggests using the metisfw/paypal package instead.
Kdyby/PayPalExpress requires PHP 5.3.2 or higher with curl enabled.
The best way to install Kdyby/PayPalExpress is using Composer:
$ composer require kdyby/paypal-express:@devLearn more in the documentation.
Homepage http://www.kdyby.org and repository http://github.com/kdyby/PayPalExpress.