Asp.net Web Api. Post a complex model to Controller and received model incorrect

I have a problem with Post a complex model object from client to Web Api controller. My Model structure is:

 public class PaymentModel
 {
    public Credit Crediter { get; set; }
 }

public class Credit : ICredit
{
    public int BankInformationId { get; set; }
}
public interface ICredit
{

    int BankInformationId { get; set; }
}
public sealed class CrediterEmployee:Credit
{
    public int EnployeeId { get; set; }
}

I tried to create a model to post to API controller:

 var param=new PaymentModel
            {
               Crediter = new CrediterEmployee
                {
                    BankInformationId = 4928,
                    EnployeeId = 7013
                },
          }

In API controller i received a model object, but for Crediter i cannot cast to CreditEmployee. It is null when i tried to cast.

How can i cast Crediter to the CreditEmployee?