RewardCircle and ReferralCodes are two brands for the same profile. Your profile name stays the same on both and can be used interchangeably, so referralcodes.com/yourname and rewardcircle.com/yourname are the same person. You do not need a second account. They are two different ways to share your support for brands — you can use both, or either one on its own.
ReferralCodes leads with the referrals you share. RewardCircle is the other way to share that same content, with the focus on earning from Circle Rewards. On RewardCircle, reviews and recommendations are shown first on all displays, including your profile and brand pages. If you joined on ReferralCodes, the toggle on your profile switches you between the two views and you can switch back any time. Circle Rewards work from either view: when someone follows your review or recommendation and completes a qualifying purchase, you can earn a reward in addition to any referral reward the brand already offers.