@Henk Visscher preassigning a lot batch no is not possible at PO Line level. For each PO Line you could have multiple PO Receipts - thus multiple lot-batch-no.
If your inventory part is has lot-batch tracking - Order Based then the lot batch will be assigned automatically for each receipt → PO-POLineNo-ReceiptNo.
I just checked in the backend and LOT_BATCH_NO is not a field in PURCHASE_ORDER_LINE_TAB. However, in PURCHASE_ORDER_LINE_API there a function Get_Lot_Batch_No which should return the next lot batch no based on PO and Line No → basically it will guess what your next receipt will be for the PO Line.
I hope this helps.
FUNCTION Get_Lot_Batch_No (
   order_no_   IN VARCHAR2,
   line_no_    IN VARCHAR2,
   release_no_ IN VARCHAR2 ) RETURN VARCHAR2
IS
   lot_batch_no_     PURCHASE_ORDER_LINE_TAB.lot_batch_no%TYPE;
   po_line_part_rec_ Purchase_Order_Line_Part_API.Public_Rec;
   lot_tracking_db_  VARCHAR2(30);
BEGIN
   po_line_part_rec_ := Purchase_Order_Line_Part_API.Get(order_no_, line_no_, release_no_);
   lot_tracking_db_  := Part_Catalog_API.Get_Lot_Tracking_Code_Db(po_line_part_rec_.part_no);
   IF (po_line_part_rec_.part_no IS NOT NULL) THEN
      IF (Is_Inventory_Part(order_no_, line_no_, release_no_) = 1) THEN
         IF (po_line_part_rec_.order_code = 6 AND ( lot_tracking_db_ != 'NOT LOT TRACKING')) THEN
            lot_batch_no_ := NVL(po_line_part_rec_.lot_batch_no, Receive_Order_API.Get_Next_Lot_Batch_No(order_no_, line_no_));
         ELSIF (lot_tracking_db_  = 'ORDER BASED') AND (Is_Intersite_Intra_Company(order_no_, line_no_, release_no_) = Fnd_Boolean_API.DB_FALSE) THEN
            lot_batch_no_ := Receive_Order_API.Get_Next_Lot_Batch_No(order_no_, line_no_);
         ELSE
            lot_batch_no_ := '*';
         END IF;
      END IF;
   END IF;
   RETURN lot_batch_no_;
END Get_Lot_Batch_No;
 
                
     
                                    
            @Henk Visscher This Lot/Batch No field is for use on a Purchase Order with an Order Type of 6, for External Service Order. If the part is configured on the Supplier for PP page for External Service and is also configured as a Sales Part, the Lot/Batch No. field on the line can be populated through a List of Values.
                
     
                                    
            Thank you for helping out, Matt & Marcel.