I'm using springboot data jpa .I have generationtype.identity but still I'm getting duplicate key for id exception.

@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
public class Order {
    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private String orderId;
    // PENDING , DISPATCHED
    private String orderStatus;
    // NOT-PAID , PAID
    private boolean paymentStatus;
    private double orderBill;
    private LocalDate orderedDate;
    private LocalDate deliveredDate;
    @ManyToOne(cascade = CascadeType.PERSIST , fetch = FetchType.EAGER)
    private User user;
    @OneToMany(cascade = CascadeType.ALL , fetch = FetchType.LAZY)
    private Set<orderitem> orderItems = new LinkedHashSet<>();
    @OneToOne(cascade = CascadeType.PERSIST)
    private BillingAddress billingAddress;

}


@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Entity
public class OrderItem {
    @Id()
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    private int count = 1;
    private double itemBill;
    @OneToOne
    private Product product;
    @ManyToOne()
    private Order order;
    
}

//This is the Service method that produces the exception on the line where I try to save Order to the database:

 public OrderDto proceedToCheckout(String userId) {
        User user  = userService.checkUserExists(userId);
        List<order> orders =  user.getOrderHistory();
        for(Order order : orders)
        {
            if(!order.isPaymentStatus())
            {
                throw new BadRequestApiException("You already have 1 order pending. Please clear that order first" +
                        " before creating a new order");
            }
        }
        Cart userCart = user.getMyCart();
        if(userCart == null)
        {
            throw new BadRequestApiException("Your cart is empty.");
        }
        Set<cartitem> cartItems = userCart.getCartItemSet();
        Order order = new Order();
        order.setUser(user);
        order.setOrderedDate(LocalDate.now());
        order.setOrderStatus("pending");
        order.setPaymentStatus(false);
        order.setOrderBill(userCart.getTotalBill());
        if(user.getBillingAddress() == null)
        {
            throw new ResourceNotFoundException("Please fill the Billing address first" +
                    " before creating your order");
        }
        order.setBillingAddress(user.getBillingAddress());
        Set<orderitem> orderItems= order.getOrderItems();
        Iterator<cartitem> it = cartItems.iterator();
        while(it.hasNext())
        {
            CartItem cartItem = it.next();

            OrderItem orderItem = new OrderItem();
            orderItem.setOrder(order);
            orderItem.setItemBill(cartItem.getItemBill());
            orderItem.setCount(cartItem.getCount());
            orderItem.setProduct(cartItem.getProduct());
            orderItems.add(orderItem);
            logger.info("orderItem in this order : {}" , orderItem.getId());
        }
        orders.add(order);
        logger.info("New Order Id = {}" , order.getOrderId());
        Order savedOrder = orderRepository.save(order);

        return modelMapper.map(savedOrder , OrderDto.class );
    }