E-commerce website add to cart function error using flask

Question

def get_product_by_id(product_id):
    cur = mysql.connection.cursor(MySQLdb.cursors.DictCursor)
    cur.execute('SELECT * FROM products WHERE id = %s', (product_id,))
    product = cur.fetchone()
    cur.close()
    if product:
        return {'id': product[0], 'name': product[1], 'description': product[2], 'price': product[3], 'image': product[4]}
    return None

@app.route('/ecommerce')
def ecommerce():
    cur = mysql.connection.cursor(MySQLdb.cursors.DictCursor)
    cur.execute('SELECT id, name, description, price, image FROM products')
    products = cur.fetchall()
    cur.close()
    return render_template('ecom.html', products=products)

@app.route('/add_to_cart/<int:product_id>', methods=['POST'])
def add_to_cart(product_id):
    try:
        # Retrieve the product information from the database using the get_product_by_id function
        product = get_product_by_id(product_id)
        if product is None:
            return "Product not found."

        # Check if the user is logged in
        if 'user_id' not in session:
            # If the user is not logged in, redirect them to the login page
            return redirect(url_for('login'))

        # Check if the cart already exists for the user
        cur = mysql.connection.cursor()
        cur.execute('SELECT * FROM cart WHERE user_id = %s', (session['user_id'],))
        cart = cur.fetchone()

        if cart is None:
            # If the cart does not exist, create a new one
            cur.execute('INSERT INTO cart (user_id, product_id, quantity, name, price) VALUES (%s, %s, %s, %s, %s)', (session['user_id'], product['id'], 1, product['name'], product['price']))
            mysql.connection.commit()
            cart_id = cur.lastrowid
        else:
            cart_id = cart['id']

        # Check if the product is already in the cart
        cur.execute('SELECT * FROM cart_items WHERE cart_id = %s AND product_id = %s', (cart_id, product['id']))
        cart_item = cur.fetchone()

        if cart_item is None:
            # If the product is not already in the cart, add it
            cur.execute('INSERT INTO cart_items (cart_id, product_id, quantity) VALUES (%s, %s, %s)', (cart_id, product['id'], 1))
        else:
            # If the product is already in the cart, update the quantity
            cur.execute('UPDATE cart_items SET quantity = quantity + 1 WHERE cart_id = %s AND product_id = %s', (cart_id, product['id']))

        mysql.connection.commit()
        cur.close()

        print("Product added to cart successfully.")
        return redirect(url_for('ecommerce'))
    except Exception as e:
        print(f"Error adding product to cart: {e}")
        return f"An error occurred while adding the product to the cart: {e}"

This was my code to implement the add to cart function so that i can see the cart in view cart but when i click on add to cart the exception says "An error occurred while adding the product to the cart: 0" i am not able to understand where is the error in the code i just want that whwn i click on add to cart then it should show the product in the view cart webpage