A store order arrives as a deal with catalog lines
When a buyer places an Order, Shopify fires orders/create. Krokul finds the contact by e-mail or phone, opens a deal in the pipeline you picked and matches each line item to a Krokul product by its SKU. The deal carries the order currency and total, the lines reserve stock in Krokul, and the Shopify order ID stays on the deal as its external key.