To verify your purchases and referrals, we ask you to link at least 1 card to the app to offer you rewards-- when you pay or refer a friend to one of btwn vendors, we track and match these actions from our end. Think of us as a digital wallet service that securely stores your payment info. To learn more about our security, read the following FAQ page: How is my card secure with btwn? Furthermore, businesses end up receiving fraudulent referrals from users that have never shopped at their store. To protect the integrity of our referral system, we require you link your card to earn rewards.