This is what your buyer sees
The page below is the one Shopify shows between the payment and the order confirmation. Click the buttons. Accepting adds the item to the order that was just placed. Declining brings up the downsell, which is where a large part of post-purchase revenue actually comes from.
Nothing here charges anything. It is a faithful reproduction of the buyer screen, not a live store, because Shopify only renders that page after a real payment.
One-time offer, before your confirmation
Leather Strap Watch
Brown · 40 mm
€39.00 €79.00 −50%
Charged to the card you just used. Ships with order #1042.
Accepted. One more, then we are done.
Polarised Sunglasses
Black
€29.00 €49.00 −41%
Still the same order. Still no second checkout.
Declined. Here is the downsell.
Leather Strap Watch
Brown · 40 mm
€29.00 €39.00 last chance
Same product, better price. The buyer who said no is a different buyer from the one who said yes, and the app knows which is which.
Added to order #1042.
No second checkout, no card re-entered, one parcel. The merchant just sold again on traffic that was already paid for.
Order #1042 confirmed.
Nothing was added, and nothing was lost. The sale was already banked before the offer appeared, which is why this is the only upsell that cannot cost a merchant the order.
What you just clicked through
Three levels, seven offers, and every offer branches twice: one path for a buyer who accepted, one for a buyer who declined. Targeting on order total or on what was in the cart. And when Shopify skips that page, which it does on Apple Pay, Google Pay and PayPal, the offer moves to the thank-you page instead, so the order still gets one.