Please make sure you are copy-pasting the full and complete registration token into the field and follow the domain provided in the email it arrived in.
Also please check you haven't already redeemed the token yourself - it may not have appeared to redeem successfully, but if you have attempted to register it previously then it may have gone through at our end, and therefore you will be unable to register it again.
If you received your registration token from someone other than us, please check it with them and make sure they provided you the complete code, and that they didn't accidentally provide you a code that had already been used by someone else.
If your token never arrived, you may not have verified your email. After you completed the registration, you would have been sent a verification email to click a link in to show that you can receive our communications. Until you click that link, your registration is not considered complete. Please check your email and double-check your spam and junk mail for this email, and make sure you click the provided link. After you click this link, it may take up to 24 hours to receive your registration token if your application is approved.