Ссылка на объект не указывает на экземпляр класса - C#

try
            {
                SmppClient client = new SmppClient();
                SmppConnectionProperties properties = new SmppConnectionProperties();
                //properties = client.Properties;
                //SmppConnectionProperties properties = client.Properties;
                properties.SystemID = textBox3.Text;
                properties.Password = textBox4.Text;
                properties.Port = Convert.ToInt32(textBox2.Text); //IP port to use
                properties.Host = textBox1.Text; //SMSC host name or IP Address
                properties.SystemType = "SMPP";
                properties.DefaultServiceType = "SMPP";
 
                //Resume a lost connection after 30 seconds
                client.AutoReconnectDelay = 3000;
 
                //Send Enquire Link PDU every 15 seconds
                client.KeepAliveInterval = 15000;
 
                //Start smpp client
                client.Start();
 
                TextMessage msg = new TextMessage();
 
                msg.DestinationAddress = textBox6.Text; //Receipient number
                msg.SourceAddress = "SMS"; //Originating number
                msg.Text = textBox5.Text;
                msg.RegisterDeliveryNotification = true; //I want delivery notification for this message
 
                //SmppClient client = GetSmppClient();
                client.SendMessage(msg);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }