Error: Type provided must be an Enum. Parameter name: enumType in ASP.Net

So I've been using the Pay Simple SDK. I'm getting this error. in line . Can anyone know how to solve this?? 

var customerPayment = new NewCustomerPayment<CreditCard>

I know that Address is not Enum and I think it is the problem, but I don't know what type is that?string?int or something?  I cannot modify the model because it's from the SDK. What's the best solution for this?

Controller code:

[HttpPost]
[ValidateAntiForgeryToken]
public async System.Threading.Tasks.Task<ActionResult> Create(FormCollection formCollection) {
    string username = "jnjk";
    string apiKey = "khkh";
    string baseUrl = "https://sandbox-api.paysimple.com";
    var settings = new PaySimpleSdk.Models.PaySimpleSettings(apiKey, username, baseUrl);

    var paymentService = new PaymentService(settings);

    var customerPayment = new NewCustomerPayment<CreditCard>()
    {

        Customer = new Customer
        {
            FirstName = formCollection["FirstName"],
            LastName = formCollection["LastName"],
            BillingAddress = (Address)Enum.Parse(typeof(Address), formCollection["BillingAddress"])
        },

        Account = new CreditCard
        {
            CreditCardNumber = formCollection["CreditCardNumber"],
            ExpirationDate = formCollection["ExpirationDate"],
            Issuer = (Issuer)Enum.Parse(typeof(Issuer), formCollection["Issuer"])
        },

        Payment = new Payment
        {  
            Amount = int.Parse(formCollection["Amount"]),
            Cvv = formCollection["Ccv"]
        }

    };

    var newCustomerPayment = await paymentService.CreateNewCustomerPaymentAsync(customerPayment);

    return View();
}

Customer Model

public Address BillingAddress { get; set; }

Address Model class

 public class Address : IValidatable
  {
    public Address();
    public string City { get; set; }
    public CountryCode? Country { get; set; }
    public StateCode? StateCode { get; set; }
    public string StreetAddress1 { get; set; }
    public string StreetAddress2 { get; set; }
    public string ZipCode { get; set; }
  }