Check your email for one titled:
Your purchase of X qualifies for the Rebate Promo, redeem your Credits now!
The instructions would say:
Congrats, your purchase of X qualifies for the Rebate Promo. Simply open the notification for Rebate Promo (Menu > Notifications) to redeem your Y in Credits! These Credits will expire in 7 days so make sure to redeem and use them before then. You can check your Credit balance and expiration any time by visiting Menu > Balance.
Have you redeemed it?