Oxify uses a Shopify Function (the free-gift-discount function) to add gift products at zero cost when a customer crosses a threshold. Because it runs natively at checkout, it's robust against script blockers, race conditions, and double-fires.
Two layers
Cart drawer (UI)
The cart drawer renders the progress bar UI on top of the same data. What you see in the cart matches what Shopify applies at checkout — guaranteed.
Shopify Function (logic)
The Function evaluates your reward tiers against the live cart at checkout and adds the gift line item. No JavaScript hooks, no flaky timers, no risk of customers checking out without their gift.
Why this matters
No double-fires — Customers can't game it.
Survives script blockers — The Function is server-side.
Native compatibility — Shopify treats it like any other discount.