One-Click Upsell shows the customer one offer right after they pay, before the thank-you page - one tap adds it to the order they just placed (same card, no second checkout), or one tap to decline.
Two offer types:
Add Product - an extra product on top of the order.
Swap Product - replace an item with a different/upgraded version; the customer pays only the price difference (or is refunded if cheaper).
💡 Want to set one up? See Setting up One-Click Upsell in the Retain collection. It may need enabling for your store - ask your CSM if you don't see it.
Related: Why isn't my One-Click Upsell showing to customers? · How is the customer charged for a One-Click Upsell?