In order to get referral credits to automatically be applied, just make sure to visit the wallet in your referral account, and enable your credits to be automatically applied to your next subscription order.
To manually apply your wallet balance to your subscription:
Login to your Club Rebel account by clicking here.
Once signed in, select Wallet at the top of the page.
Click the copy button under "Copy and use the code below at checkout. This code will apply your wallet balance as a discount on your next order".
Go to the account page.
Enter your registered email address - this is the email you used when creating your subscription
Click Continue
You'll receive a one-time verification code via email
Enter the code on the login screen
Select Subscriptions at the top of the page
Enter your discount code you copied in the promo code field and click Apply