Check that:
the app embed is turned on in your live theme,
the campaign is active and scheduled for now,
the cart meets its rule,
the gift product is in stock and available on your online store.
When several campaigns fit a cart, their priority and stacking settings decide which ones give gifts.
Still stuck?
Open the app in your Shopify admin, go to Help and click Chat with us, or email [email protected] with your store’s myshopify.com address.