You can register Rey theme through several ways. You will however need the purchase code before you start. How to get a purchase code?
Setup wizard:
Right after you activate Rey theme the first time, you should be redirected to a setup wizard. You can find the registration form into the first step.
Rey Dashboard:
If you’re not already registered, in the Dashboard page, you should see the registration form in the first box.
Manual:
Open wp-config.php with your favorite editor and inside it, say – before or after define('WP_DEBUG', false); , please add the following constant:
define('REY_API_KEY', '00000000-0000-0000-0000-000000000000');
Deregister
If you want to deregister, access Rey theme – Dashboard and in the first box, you should see the “DEREGISTER PURCHASE CODE” button.
Getting a “Something went wrong” error:
This error can happen when the SSL certificate is not properly set into the site. First step to check this, is to access Settings in the backend and look at the Site Address and Site URL and check if they contain “https” protocol.
Dealing with localhost vs live locations when registering with the purchase code
Unfortunately even though you’re using the key on your localhost, the key cannot be simultaneously active in multiple locations, so you will need to deregister from localhost first, and then register onto the live location.
Can the purchase code be registered on a multisite instance
Yes it can. But please make sure to read this article too https://support2.reytheme.com/kb/updating-on-multisite-installations/ .