Billing Portal Configuration - Not serialising correctly (Update Products)

[AshleyMedway]

Describe the bug

When using BillingPortal.ConfigurationService the Feature SubscriptionUpdate is not sending the Products collection to the API

To Reproduce

var options = new ConfigurationCreateOptions
{
    Features = new ConfigurationFeaturesOptions
    {
        InvoiceHistory = new ConfigurationFeaturesInvoiceHistoryOptions { Enabled = true },
        PaymentMethodUpdate = new ConfigurationFeaturesPaymentMethodUpdateOptions { Enabled = true },
        SubscriptionCancel = new ConfigurationFeaturesSubscriptionCancelOptions
        {
            Enabled = true,
            Mode = "at_period_end",
            ProrationBehavior = "none",
            CancellationReason = new ConfigurationFeaturesSubscriptionCancelCancellationReasonOptions
            {
                Enabled = true,
                Options = ["customer_service", "low_quality", "missing_features", "switched_service", "too_complex", "too_expensive", "unused", "other"]
            }
        },
        SubscriptionUpdate = new ConfigurationFeaturesSubscriptionUpdateOptions
        {
            Enabled = true,
            DefaultAllowedUpdates = ["quantity", "price", "promotion_code"],
            ProrationBehavior = "create_prorations",
            Products = new List<ConfigurationFeaturesSubscriptionUpdateProductOptions>
                {
                    new ConfigurationFeaturesSubscriptionUpdateProductOptions
                    {
                        Product = "prod_xxx1",
                        Prices = ["price_xxx1"]
                    },
                    new ConfigurationFeaturesSubscriptionUpdateProductOptions
                    {
                        Product = "prod_xxx2",
                        Prices = ["price_xxx2"]
                    },
                    new ConfigurationFeaturesSubscriptionUpdateProductOptions
                    {
                        Product = "prod_xxx3",
                        Prices = ["price_xxx3", "price_xxx4"]
                    }
                },
            ScheduleAtPeriodEnd = new ConfigurationFeaturesSubscriptionUpdateScheduleAtPeriodEndOptions
            {
                Conditions =
                [
                    new ConfigurationFeaturesSubscriptionUpdateScheduleAtPeriodEndConditionOptions { Type = "decreasing_item_amount"  },
                    new ConfigurationFeaturesSubscriptionUpdateScheduleAtPeriodEndConditionOptions { Type = "shortening_interval" }
                ]
            }
        },
        CustomerUpdate = new ConfigurationFeaturesCustomerUpdateOptions
        {
            Enabled = true,
            AllowedUpdates = ["email", "tax_id", "address", "name", "phone"]
        }
    },
    DefaultReturnUrl = "https://example.co.uk",
    LoginPage = new ConfigurationLoginPageOptions { Enabled = false },
    BusinessProfile = new ConfigurationBusinessProfileOptions
    {
        Headline = "MyProduct",
        PrivacyPolicyUrl = "https://example.co.uk/privacy-policy/",
        TermsOfServiceUrl = "https://example.co.uk/terms-of-service/"
    },
    Metadata = new Dictionary<string, string>
    {
        { "type", "test" }
    }
};

var portalConfig = await service.CreateAsync(options, null, cancellationToken);

From the portalConfig result you can see that the Products under SubscriptionUpdate is null.
From the Developer Logs explorer you can see that the Products are not sent

Expected behavior

Products are sent via the API. The resulting session that is created can update the subscription.

Code snippets

OS

windows

.NET version

.NET 9.0

Library version

Stripe.net 47.4.0

API version

2025-02-24

Additional context

No response