Requires Craft 2.5+, running php 5.5.9+
All live payment pages should be served over SSL.
During development & testing, you don't need to setup any SSL certs, it's only something you'll need to do when you want to take real payments from users.
Setting up an SSL cert on your server is normally a straight-forward process. If you need a hand getting this setup drop a line into support and we'll be glad to help you get setup.
We recommend LetsEncrypt as a reliable and free source of getting your SSL Certs.