Merge the thank you page upsell with the main order & ship only once
1. Enable merging orders. The main order and the thank you page upsell order are canceled, but not refunded, and merged into a new order. This allows to skip the first two steps of checkout (customer details and shipping) and to offer free shipping on the upsell order. If you disable this option, two independent orders will be created.
2. By default, when customers accept the thank you page upsell, the main order and the upsell order are cancelled and merged into a single order shipped once. However, Shopify tracks all 3 orders as successfully paid separately. If you enable this option, only the main order and the upsell order will be tracked in the sales reports.