If you are trying to register Free licenses, you should keep in mind that they vary between the versions, i.e. there is a set of them for Ray 3.0 and another one for 3.1. You should see the combo box with versions to choose next to "Get Free licenses" button.

So if you have installed Ray 3.0 you should use licenses generated for 3.0 version.
The same applies to the 3.1 licenses set. They should be applied to appropriate 3.1 Ray Package on your site.