The scenario described is an example of a marketing strategy known as a loyalty reward
What explains the scenario
Specifically, it falls under the category of customer loyalty programs. In this case, VF Corporation, the company from which Haley often purchases clothes online, is rewarding her loyalty and celebrating her birthday by sending her an email birthday card with a voucher for $20 off on her next online purchase.
Customer loyalty programs are designed to encourage repeat business by providing incentives, rewards, or special offers to customers who consistently choose a particular brand or company for their purchases.