It is not uncommon to find limitations, which may touch on the number of times the cardholder uses the referral code and the amount of reward that he or she can receive within any given time. Referral can only be new, the referred card type should not be in the referral’s possession and should sign up through the referral link. The program may also be amended or cancelled at any time without notice, and usually the rewards are given based on the specific terms, such as after the referred friend’s account has been approved and once he/she has spent the required amount.
Source: https://probabs.com/capital-one-refer-a-friend/