When a guest attempts to redeem an expired redeemable or a redeemable that has been removed from the admin panel, they will see this error message(or you may see it within Support > Redemptions Failures. This situation occurs when a redeemable has been deactivated/expired but remains visible in the Push Notifications the guest can see in their app.
Note: This is why it is important to set the time the redeemable will be removed from a guest's Push Notifications.
This may also occur if an upper limit on the number of rewards available has been exceeded. For example, if the reward is a free hat limited to the first 10,000 guests and a guest attempts to redeem that reward after that number limit has been reached, they may receive this message.