What happens when more shoppers find a gift than my coupon limit allows?

In Plugins → Find & Earn → Events, click Manage on the event and set the limits:

• Item coupon limit on each gift (in the Gifts section) caps how many shoppers can win that gift's coupon.
• Completion coupon limit in Completion reward caps how many can win the prize for finding all gifts.

Once a limit is reached, later finders still open the gift but see the Item coupon limit reached or Completion coupon limit reached message in place of a coupon. You can reword those messages in Plugins → Find & Earn → Settings.

Make sure the coupon codes exist in Marketing → Coupons, with usage limits that match.