I use firstdata webservice API.I use C# client call firstdata webservice API with WCF. But show error message: "But show error message "System.ServiceModel.Security.MessageSecurityException: The HTTP request is unauthorized with client authentication scheme 'Anonymous'. The authentication header received from the server was ''. --- System.Net.WebException: The remote server returned an error: (401) Unauthorized. at System.Net.HttpWebRequest.GetResponse() at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) --- End of inner exception stack trace --- Server stack trace: at System.ServiceModel.Channels.HttpChannelUtilities.ValidateAuthentication(HttpWebRequest request, HttpWebResponse response, WebException responseException, HttpChannelFactory factory) at System.ServiceModel.Channels.HttpChannelUtilities.ValidateRequestReplyResponse(HttpWebRequest request, HttpWebResponse response, HttpChannelFactory factory, WebException responseException, ChannelBinding channelBinding) at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) at System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout) at System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message message, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation) at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at com.firstdata.globalgatewaye4.api.ServiceSoap.SendAndCommit(SendAndCommitRequest request) at com.firstdata.globalgatewaye4.api.ServiceSoapClient.com.firstdata.globalgatewaye4.api.ServiceSoap.SendAndCommit (SendAndCommitRequest request) at com.firstdata.globalgatewaye4.api.ServiceSoapClient.SendAndCommit(Transaction SendAndCommitSource)" My web.config info below: <behaviors> <endpointBehaviors> <behavior name="FDGGBehavior"> <clientCredentials> <clientCertificate findValue="WS1909642825._.1" storeLocation="LocalMachine" x509FindType="FindBySubjectName" storeName="TrustedPeople" /> <serviceCertificate> <authentication certificateValidationMode="PeerTrust" /> </serviceCertificate> </clientCredentials> </behavior> </endpointBehaviors> </behaviors> <binding name="ServiceSoap" closeTimeout="00:01:00" openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:01:00" allowCookies="false" bypassProxyOnLocal="false" hostNameComparisonMode="StrongWildcard" maxBufferSize="65536" maxBufferPoolSize="524288" maxReceivedMessageSize="65536" messageEncoding="Text" textEncoding="utf-8" transferMode="Buffered" useDefaultWebProxy="true"> <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384" maxBytesPerRead="4096" maxNameTableCharCount="16384" /> <security mode="TransportWithMessageCredential"> <transport clientCredentialType="Certificate" proxyCredentialType="Ntlm" /> <message clientCredentialType="UserName" algorithmSuite="Default" /> </security> </binding> <endpoint address="https://api.globalgatewaye4.firstdata.com/transaction/v11" binding="basicHttpBinding" bindingConfiguration="ServiceSoap" contract="com.firstdata.globalgatewaye4.api.ServiceSoap" name="ServiceSoap" behaviorConfiguration="FDGGBehavior" /> How can resolve question?