In order to earn commissions, you will need to have users sign up for your whitelabeled site. To do this, you can send them to the site in a number of ways.
Send them to the main RxSpark domain with ?ref=[your_code] at the end of the URL. This will brand the site to you, but maintain the original RxSpark URL
Send them your custom domain.
Send them to your landing page. You can find the link to your landing page in the Partner Portal under "Landing Pages"
Register them via the API (API Reference)