var message = new Message
{
   message_conv_id = conv_id,
   message_conv_type = TIMConvType.kTIMConv_C2C,
   message_elem_array = new List<Elem>{new Elem
   {
     elem_type = TIMElemType.kTIMElem_Custom,
     custom_elem_data = "Typing..."
   }},
   message_is_online_msg = true
};
 StringBuilder messageId = new StringBuilder(128);
 TIMResult res = TencentIMSDK.MsgSendMessage(conv_id, TIMConvType.kTIMConv_C2C, message, messageId, (int code, string desc, Message data, string user_data) => {
  // Process the callback logic
 });