System.FormatException: Input string was not in a correct format when deserializing xml

Question

I'm trying to post a cart to the prestashop webservice and I'm getting a deserializer error when trying to get the blank cart. I've red that you get the blank cart from the api (instead of building it from a constructor), then populate it, and finally post it. But when I try to get the blank cart i get the following error:

Microsoft.Bot.Builder.Integration.AspNet.Core.BotFrameworkHttpAdapter:Error: Exception caught : System.InvalidOperationException: There is an error in XML document (4, 11). ---> System.FormatException: Input string was not in a correct format.
   at System.Number.StringToNumber(ReadOnlySpan`1 str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
   at System.Number.ParseInt32(ReadOnlySpan`1 s, NumberStyles style, NumberFormatInfo info)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderPrestashopCart.Read6_Cart(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderPrestashopCart.Read7_PrestashopCart(Boolean isNullable, Boolean checkType)
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderPrestashopCart.Read8_prestashop()
   --- End of inner exception stack trace ---

I've red here that that's due to some tag missing value, but here all the tags have empty values and the error doesn't pop until the 11th line, so I don't know why it means.

The xml:

<?xml version="1.0" encoding="UTF-8"?>
<prestashop xmlns:xlink="http://www.w3.org/1999/xlink">
<cart>
    <id></id>
    <id_address_delivery></id_address_delivery>
    <id_address_invoice></id_address_invoice>
    <id_currency></id_currency>
    <id_customer></id_customer>
    <id_guest></id_guest>
    <id_lang></id_lang>
    <id_shop_group></id_shop_group>
    <id_shop></id_shop>
    <id_carrier></id_carrier>
    <recyclable></recyclable>
    <gift></gift>
    <gift_message></gift_message>
    <mobile_theme></mobile_theme>
    <delivery_option></delivery_option>
    <secure_key></secure_key>
    <allow_seperated_package></allow_seperated_package>
    <date_add></date_add>
    <date_upd></date_upd>
<associations>
<cart_rows>
    <cart_row>
    <id_product></id_product>
    <id_product_attribute></id_product_attribute>
    <id_address_delivery></id_address_delivery>
    <quantity></quantity>
    </cart_row>
</cart_rows>
</associations>
</cart>
</prestashop>

The deserializer class:

    [XmlRoot("prestashop")]
    public class PrestashopCart
    {
        [XmlElement("cart")]
        public Cart Cart { get; set; }
    }


public class Cart : IIdentifiable
    {
        [XmlElement("id")]
        public override int Id { get; set; }

        [XmlElement("id_address_delivery")]
        public int DeliveryAddressId { get; set; }

        [XmlElement("id_address_invoice")]
        public int AdressInvoiceId { get; set; }

        [XmlIgnore]
        public Customer Customer { get; set; }

        private int? _customerId { get; set; }

        [XmlElement("id_currency")]
        public int CurrencyId { get; set; }

        [XmlElement("id_customer")]
        public int CustomerId
        {
            get { return _customerId ?? Customer.Id; }
            set { _customerId = value; }
        }

        [XmlElement("id_guest")]
        public int GuestId { get; set; }

        [XmlElement("id_lang")]
        public int LanguageId { get; set; }

        [XmlElement("id_shop_group")]
        public int? ShopGroupId { get; set; }

        [XmlElement("associations")]
        public CartRowCollection Rows { get; set; }
    }

There's some xml tags missing, that's because I don't need these fields.