You can set up the supply source for the Kanban process in SAP S/4HANA by using different replenishment strategies, depending on whether the material is procured internally or externally. For internal procurement, you can use run schedule quantities, which are calculated based on the Kanban quantity and the number of Kanbans. For external procurement, you can use purchase orders, which are created automatically when a Kanban status changes to EMPTY. For stock transfer, you can use stock transfer reservations, which are also created automatically when a Kanban status changes to EMPTY and trigger a goods movement from the supplying plant to the receiving plant. References: Replenishment Strategies, Stock Transfer with Kanban, External Procurement with Kanban