Orders that contain products from the retailer's store, as well as a supplier's store, are called Mixed Cart Orders.
When retailers receive a Mixed Cart Order, the supplier's products are separated within the order itself to provide clarity on what needs to be fulfilled and by who.
The supplier's portion of the order is automatically routed to them for fulfillment.
The customer will receive separate emails with separate tracking information once the retailer and supplier fulfill their portions of the order. To learn more about this, please refer to this article.