metadata empty when retrieving a Checkout Session's line items

Describe the bug

Hello everyone, I've created a stripe checkout session and in the line_items property I'm passing the products I receive from the request's body. In the product_data of each product I added a metadata that contains the product's id. Then I created a webhook that listens to the checkout.session.completed event type, where I retrieve the line_items so that I can create an order document (because I'm working with mongoose) and save it in my database. The problem is: I can't find the id I defined in each product's metadata.

To Reproduce

N/A

Expected behavior

When retrieving the line_items and looping through the data property, I expect to find the id I defined in the metadata of each product.

Code snippets

// creating a checkout session
try {
        const cart: ICart[] = req.body.cart;
        const accountEmail: string = req.body.account;
        const tax: number = req.body.tax;
        const discountId: string = req.body.discount; 

        const cartItems: Stripe.Checkout.SessionCreateParams.LineItem[] =
            cart.map((item): Stripe.Checkout.SessionCreateParams.LineItem => {
                return {
                    price_data: {
                        currency: "mad",
                        product_data: {
                            name: item?.name,
                            description: item?.description,
                            images: item?.images,
                            metadata: { id: item?._id },
                        },
                        unit_amount: item?.amount * 100,
                    },
                    quantity: item?.quantity,
                };
            });

        // create the checkout session
        const session = await stripe.checkout.sessions.create({
            currency: "mad",
            ui_mode: "hosted",
            line_items: [
                ...(cartItems as Stripe.Checkout.SessionCreateParams.LineItem[]),
            ],
            billing_address_collection: "required",
            mode: "payment",
            customer_email: accountEmail,
            metadata: {
                email: accountEmail,
                tax: tax,
                discount: discountId,
            },
            success_url: `${env.APP_URL}/success?session_id={CHECKOUT_SESSION_ID}`,
            cancel_url: `${env.APP_URL}/success?session_id={CHECKOUT_SESSION_ID}`,
        });
        res.status(200).json({
            status: "success",
            session,
            clientSecret: session.client_secret,
        });
} catch (err) {
        console.log(err);
}

// in the webhook's swith case
// retrieving the line items
case "checkout.session.completed":
      const checkoutSessionCompleted = event.data.object;

      // Retrieve the session's line items
      const lineItems = (await stripe.checkout.sessions.listLineItems(checkoutSessionCompleted.id)).data.map((item) => {
      return {
              _id: item.price?.metadata?.id, // returns undefined
              quantity: item.quantity, // returns the quantity
             }
         });

OS

Wndows

Node version

Node v21.2.0

Library version

stripe-node v14.11.0

API version

2023-10-16

Additional context

No response

stripe / stripe-node