Preorder Back In Stock adds a preorder button or a Notify me when available waitlist to every sold-out product, without touching your theme. Run campaigns with full or partial-deposit payments, percent or fixed discounts, scheduled start and end, variant and collection targeting, and per-campaign translations. Back-in-stock subscribers are emailed when inventory hits your threshold. Built on Polaris with a 3-step wizard, live preview, conflict detection, order tags, and GDPR consent.