Issue with Web API Model Binding: Object passed to service is null only on iOS.

Hello All.

I have been running into a very strange issue, and I am not even sure if this is an issue with my app or the web service I am calling.

I have a Web Api Service with a Post method that accepts a complex parameter (it is my own custom object). In my Xamarin project I have some pretty straightforward code to call this service:

public async Task SubmitEReport(decimal amount, DateTime receivedDate, byte[] image)
{
try
{
HttpClient client = new HttpClient();

            var uri = new Uri("https://services.example.com/EPub/api/Expense/");

            var eReport = new eReport()
            {
                UserName = "EMPLOYEE\" + Application.Current.Properties["username"].ToString(),
                Cost = amount,
                ReceivedDate= receivedDate,
                ReceiptImageExtension = "jpg",
                SubmittalDate = DateTime.Now,
                Image = image
            };

            var json = JsonConvert.SerializeObject(eReport );

            var content = new System.Net.Http.StringContent(json, Encoding.UTF8, "application/json");

            content.Headers.Add("authorize-token", Application.Current.Properties["auth-token"] as string);

            HttpResponseMessage response = null;

            response = await client.PostAsync(uri, content);

            var eResult = new EResult()
            {
                Success = response.IsSuccessStatusCode,
                ErrorMessage = response.ReasonPhrase


            };

            return eResult ;
        }
        catch (Exception ex)
        {
            var errorResult = new eResult () { Success = false, ErrorMessage = ex.Message };
            return errorResult;
        }
    }

The issue that I am having is that, when I test this on an Android the code works as expected: the service is called, the object passed over is not null and has the data in it. In short, the parameter binding works as expected. The same is not so on iOS: when I call the service using the app on an iPhone, I can see that it is reaching the service and the Post method, but the parameter binding is not working correctly as the object I am passing over is always null.

Any help is appreciated.