API to Cancel Sales Order In Oracle APPS R12

 DECLARE

    v_api_version_number         NUMBER := 1;
    v_return_status              VARCHAR2 (2000);
    v_msg_count                  NUMBER;
    v_msg_data                   VARCHAR2 (2000);
    -- IN Variables --
    v_header_rec                 oe_order_pub.header_rec_type;
    v_line_tbl                   oe_order_pub.line_tbl_type;
    v_action_request_tbl         oe_order_pub.request_tbl_type;
    v_line_adj_tbl               oe_order_pub.line_adj_tbl_type;
    -- OUT Variables --
    v_header_rec_out             oe_order_pub.header_rec_type;
    v_header_val_rec_out         oe_order_pub.header_val_rec_type;
    v_header_adj_tbl_out         oe_order_pub.header_adj_tbl_type;
    v_header_adj_val_tbl_out     oe_order_pub.header_adj_val_tbl_type;
    v_header_price_att_tbl_out   oe_order_pub.header_price_att_tbl_type;
    v_header_adj_att_tbl_out     oe_order_pub.header_adj_att_tbl_type;
    v_header_adj_assoc_tbl_out   oe_order_pub.header_adj_assoc_tbl_type;
    v_header_scredit_tbl_out     oe_order_pub.header_scredit_tbl_type;
    v_header_scredit_val_tbl_out oe_order_pub.header_scredit_val_tbl_type;
    v_line_tbl_out               oe_order_pub.line_tbl_type;
    v_line_val_tbl_out           oe_order_pub.line_val_tbl_type;
    v_line_adj_tbl_out           oe_order_pub.line_adj_tbl_type;
    v_line_adj_val_tbl_out       oe_order_pub.line_adj_val_tbl_type;
    v_line_price_att_tbl_out     oe_order_pub.line_price_att_tbl_type;
    v_line_adj_att_tbl_out       oe_order_pub.line_adj_att_tbl_type;
    v_line_adj_assoc_tbl_out     oe_order_pub.line_adj_assoc_tbl_type;
    v_line_scredit_tbl_out       oe_order_pub.line_scredit_tbl_type;
    v_line_scredit_val_tbl_out   oe_order_pub.line_scredit_val_tbl_type;
    v_lot_serial_tbl_out         oe_order_pub.lot_serial_tbl_type;
    v_lot_serial_val_tbl_out     oe_order_pub.lot_serial_val_tbl_type;
    v_action_request_tbl_out     oe_order_pub.request_tbl_type;
    CURSOR c1 IS
      SELECT (SELECT order_number
              FROM   oe_order_headers_all
              WHERE  header_id = ool.header_id)order_num,
             header_id,
             line_id,
             ordered_quantity
      FROM   oe_order_lines_all
      WHERE  header_id = (SELECT header_id
                          FROM   oe_order_headers_all
                          WHERE  order_number = <------->)
             AND flow_status_code = 'AWAITING_SHIPPING';
BEGIN
    dbms_output.Put_line('Starting of script');

    -- Setting the Enviroment --
    mo_global.Init('ONT');

    fnd_global.Apps_initialize (user_id => 0,resp_id => ----,resp_appl_id => 660);

    mo_global.Set_policy_context('S', 105);

    V_action_request_tbl (1) := oe_order_pub.g_miss_request_rec;

    FOR ord_rec IN c1 LOOP
        -- Cancel a Line Record --
        V_line_tbl (1) := oe_order_pub.g_miss_line_rec;

        V_line_tbl (1).operation := oe_globals.g_opr_update;

        V_line_tbl (1).header_id := ord_rec.header_id;

        V_line_tbl (1).line_id := ord_rec.line_id; --12.2

        V_line_tbl (1).ordered_quantity := ord_rec.ordered_quantity;

        V_line_tbl (1).cancelled_flag := 'Y';

        V_line_tbl (1).change_reason := 'Canceled Through API';

        dbms_output.Put_line('Starting of API for Line Id'
                             ||ord_rec.line_id);

        -- Calling the API to cancel a line from an Existing Order --
        oe_order_pub.Process_order (p_api_version_number => v_api_version_number
        ,
        p_header_rec => v_header_rec, p_line_tbl => v_line_tbl,
        p_action_request_tbl => v_action_request_tbl,
        p_line_adj_tbl => v_line_adj_tbl
        -- OUT variables
        , x_header_rec => v_header_rec_out,
        x_header_val_rec => v_header_val_rec_out
        ,
        x_header_adj_tbl => v_header_adj_tbl_out,
        x_header_adj_val_tbl => v_header_adj_val_tbl_out,
        x_header_price_att_tbl => v_header_price_att_tbl_out,
        x_header_adj_att_tbl => v_header_adj_att_tbl_out,
        x_header_adj_assoc_tbl => v_header_adj_assoc_tbl_out,
        x_header_scredit_tbl => v_header_scredit_tbl_out,
        x_header_scredit_val_tbl => v_header_scredit_val_tbl_out,
        x_line_tbl => v_line_tbl_out, x_line_val_tbl => v_line_val_tbl_out,
        x_line_adj_tbl => v_line_adj_tbl_out,
        x_line_adj_val_tbl => v_line_adj_val_tbl_out,
        x_line_price_att_tbl => v_line_price_att_tbl_out,
        x_line_adj_att_tbl => v_line_adj_att_tbl_out,
        x_line_adj_assoc_tbl => v_line_adj_assoc_tbl_out,
        x_line_scredit_tbl => v_line_scredit_tbl_out,
        x_line_scredit_val_tbl => v_line_scredit_val_tbl_out,
        x_lot_serial_tbl => v_lot_serial_tbl_out,
        x_lot_serial_val_tbl => v_lot_serial_val_tbl_out,
        x_action_request_tbl => v_action_request_tbl_out,
        x_return_status => v_return_status, x_msg_count => v_msg_count,
        x_msg_data => v_msg_data);

        dbms_output.Put_line('Completion of API for line id'
                             ||ord_rec.line_id);

        IF v_return_status = fnd_api.g_ret_sts_success THEN
          COMMIT;

          dbms_output.Put_line ('Line Cancelation in Existing Order is Success '
          );
        ELSE
          dbms_output.Put_line ('Line Cancelation in Existing Order failed:'
                                ||v_msg_data);

          ROLLBACK;

          FOR i IN 1 .. v_msg_count LOOP
              v_msg_data := oe_msg_pub.Get(p_msg_index => i, p_encoded => 'F');

              dbms_output.Put_line(i
                                   || ') '
                                   || v_msg_data);
          END LOOP;
        END IF;
    END LOOP;
END; 

Note: If there is any issue with Sales Order Line Cancellation through above API, then we may also try below DMLs. Kindly make sure there is no any RESERVATION Quantity against those Lines :

UPDATE ont.oe_order_lines_all
SET    flow_status_code = 'CANCELLED',
       cancelled_flag = 'Y',
       cancelled_quantity = ordered_quantity
       --ORDERED_QUANTITY = 0
WHERE  line_id IN (<-------------->);

SELECT wdd.released_status,
       wdd.*
FROM   oe_order_headers_all h,
       oe_order_lines_all l,
       wsh_delivery_details wdd,
       wsh_delivery_assignments wda
WHERE  h.header_id = l.header_id
AND    wdd.source_header_id = l.header_id
AND    wdd.source_line_id = l.line_id
AND    wdd.delivery_detail_id = wda.delivery_detail_id
AND    h.order_number = <------>
AND    wda.delivery_id = <----->;

UPDATE wsh_delivery_details
SET    released_status = 'D' --D: Cancelled -Line is Cancelled
WHERE  delivery_detail_id = <---->;