There are two common ways our existing users do it:
👉 Source store sends invoice to destination store and then destination store makes payment. If orders module is enabled, then source store can filter orders by the destination store as a quick way to find the orders sent by destination store. If orders module is not enabled, source store will need to rely on the manual order sent from the destination store.
👉 Source store creates a discount code that the destination uses to purchase the product ordered on the destination store so that the source store gets the order and payment. In this case, you need to turn off inventory sync.