What happens to a waiting reward if my subscription ends?

If your friend has met the conditions but you no longer have a paid subscription, a pending reward waits for a new paid subscription for up to 365 days. It expires if you do not become eligible within that time.

App Store has another case: if a reward is already available to redeem and your subscription ends before you redeem it, that offer becomes ineligible.

Check the state in You → Invite a friend. A waiting reward and an unredeemed store offer follow different rules.