Getting (415) Unsupported Media Type error

What I have to do is that I have to post JSON data in given URL Where my JSON looks like

{
    "trip_title":"My Hotel Booking",
    "traveler_info":{
        "first_name":"Edward",
        "middle_name":"",
        "last_name":"Cullen",
        "phone":{
            "country_code":"1",
            "area_code":"425",
            "number":"6795089"
        },
        "email":"asdv@gmail.com"
    },
    "billing_info":{
        "credit_card":{
            "card_number":"47135821",
            "card_type":"Visa",
            "card_security_code":"123",
            "expiration_month":"09",
            "expiration_year":"2017"
        },
        "first_name":"Edward",
        "last_name":"Cullen",
        "billing_address":{
            "street1":"Expedia Inc",
            "street2":"108th Ave NE",
            "suite":"333",
            "city":"Bellevue",
            "state":"WA",
            "country":"USA",
            "zipcode":"98004"
        },
        "phone":{
            "country_code":"1",
            "area_code":"425",
            "number":"782"
        }
    },
    "marketing_code":""
}

And my function

string message = "URL";
_body="JSON DATA";
HttpWebRequest request = HttpWebRequest.Create(message) as HttpWebRequest;
if (!string.IsNullOrEmpty(_body))
{
    request.ContentType =  "text/json";
    request.Method =  "POST";

    using (var streamWriter = new StreamWriter(request.GetRequestStream()))
    {
        streamWriter.Write(_body);
        streamWriter.Flush();
        streamWriter.Close();
    }
}

using (HttpWebResponse webresponse = request.GetResponse() as HttpWebResponse)
{
    using (StreamReader reader = new StreamReader(webresponse.GetResponseStream()))
    {
        string response = reader.ReadToEnd();
    }
}

And when I am posting it; I am getting an error

"The remote server returned an error: (415) Unsupported Media Type."

Anyb