What is causing this error message? The remote server returned an error: (422) Non-Process Organization

I am trying to send a request to a REST API using WCF; here's what i did:

namespace Sample
{
    [ServiceContract]
    [XmlSerializerFormat]
    public interface ISampleApi
    {
        [OperationContract]
        [WebInvoke(Method = "POST", UriTemplate = "users.xml", ResponseFormat = WebMessageFormat.Xml, RequestFormat = WebMessageFormat.Xml)]
        User CreateUser(User user);
    }
}

      

        
        
        
      

    

And this is my User

class:

namespace Sample.Entity
{
    [XmlRoot("user")]
    public class User
    {
        [XmlElement("company")]
        public string Company { get; set; }

        [XmlElement("country-code")]
        public string ContryCode { get; set; }

        [XmlElement("created-at")]
        public DateTime CreatedAt { get; set; }

        [XmlElement("email")]
        public string Email { get; set; }

        [XmlElement("external-identifier")]
        public string ExternalIdentifier { get; set; }

        [XmlElement("id")]
        public int Id { get; set; }

        [XmlElement("measurement-system")]
        public string MeasurmentSystem { get; set; }

        [XmlElement("profile")]
        public string Profile { get; set; }

        [XmlElement("url")]
        public string Url { get; set; }

        [XmlElement("username")]
        public string Username { get; set; }

        [XmlElement("account-type")]
        public string AccountType { get; set; }
    }
}

      

        
        
        
      

    

But when I call the CreateUser method and pass a User object to it, I get this error message:

The remote server returned an error: (422) Non-Process Organization.

Any idea what is causing this?