An unhandled exception of type 'System.Net.WebException' occurred in System.dll

Additional information: The remote server returned an error: (400) Bad Request.

<?xml version="1.0"?>
<configuration>
    <system.web>
        <compilation debug="true" targetFramework="4.5" />
        <httpRuntime targetFramework="4.5"/>
    </system.web>
    <system.serviceModel>
        <behaviors>
            <serviceBehaviors>
                <behavior>
                    <!-- To avoid disclosing metadata information, set the values below to false before deployment -->
                    <serviceMetadata httpGetEnabled="true" httpsGetEnabled="true"/>
                    <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
                    <serviceDebug includeExceptionDetailInFaults="false"/>
                </behavior>
            </serviceBehaviors>
        </behaviors>
        <services>
            <service name="WcfService1.Service1">
                <endpoint address="Soap" binding="basicHttpBinding" contract="WcfService1.IService1" />
                <endpoint address="Http" kind="webHttpEndpoint" contract="WcfService1.IService1" />
                <endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
            </service>
        </services>
        <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
    </system.serviceModel>
    <system.webServer>
        <modules runAllManagedModulesForAllRequests="true"/>
        <httpErrors errorMode="Detailed"/>
    </system.webServer>
</configuration>

[ServiceContract]
public interface IService1
{
    [OperationContract]
    [WebInvoke]
    string GetData(string channel);
}

private static string HttpPost(string _postData)
{
    using (WebClient webClient = new WebClient())
    {
        webClient.BaseAddress = "http://localhost:62147/Service1.svc/Soap/";
        webClient.Headers.Add("Content-Type", "text/xml; charset=utf-8");
        webClient.Headers.Add("SOAPAction", "http://tempuri.org/IService1/GetData");

        byte[] response = webClient.UploadData("GetData", Encoding.UTF8.GetBytes(_postData));

        return Encoding.UTF8.GetString(response);
    }
}