This year Mt Ruapehu introduced a new website. If you haven't registered with this website before, you'll need to do so before you purchase or reload your Season Pass.
Go to the Login button at the top of the screen, then choose ‘Register’ at the bottom of that page.
Fill out all of your details and hit submit.
You’ll then receive an email to validate your account. Follow the instructions in that to activate your account.
You can then go and log in (with your password, Facebook, or Google) and your existing pass should be attached to your profile so you can reload for next season.
If this doesn’t work, feel free to purchase a new card, and bring your old one back for a refund on your next visit.