Private key is not in certificate

[dotnetclue]

Hi,
I want to ask a qusetion according to my code, My code is as bellow:
in AuthenticateAsServer I get "The server mode SSL must use a certificate with the associated private key" error cause privatekey is not in my certificate and also privatekey is not extractable from my HSM, would you please guid me what is the solution here?
Thanks inadvance

     static void ProcessClient(TcpClient client)
    {
        SslStream sslClientStream = new SslStream(client.GetStream(), true, AllowAnyServerCertificate, null, 
       EncryptionPolicy.RequireEncryption);

        try
        {
            X509Certificate2 _HsmserverCertificate = null;

            string pkcs11LibraryPath = "C:\\Program Files (x86)\\nCipher\\nfast\\toolkits\\pkcs11\\cknfast-64.dll";

            Pkcs11InteropFactories factories = new Pkcs11InteropFactories();

            using (IPkcs11Library pkcs11Library = factories.Pkcs11LibraryFactory.LoadPkcs11Library(factories, pkcs11LibraryPath, 
               AppType.MultiThreaded))
            {
                ISlot slot = HelpersMethods.GetUsableSlot(pkcs11Library);

                using (Net.Pkcs11Interop.HighLevelAPI.ISession session = slot.OpenSession(SessionType.ReadWrite))
                {
                    session.Login(CKU.CKU_USER, @"1234");

                    var certificate = ReadCertificates(slot, session)[0];

                    _HsmserverCertificate = new X509Certificate2(certificate.CkaValue);
					
                    session.Logout();
                }
            }

            sslClientStream.ReadTimeout = glb_intReciveTimeOut;
            sslClientStream.WriteTimeout = glb_intSendTimeOut;

            sslClientStream.AuthenticateAsServer(_HsmserverCertificate,
                                                 clientCertificateRequired: false,
                                                 SslProtocols.Tls12,
    }
}

---