Issue with Prepared Statement in C# with MySQL

I have created a function that takes a List of codes and some other information and attempts to insert the data into a MySQL table.  I'm trying to use a prepared statement, but for some reason the records do not actually record the code value.  Can you tell me what I am doing wrong with my approach, or is there a better way of going about this?  Code is as follows:

public static bool WriteToDatabase(IList Codes, string PONumber, string ValidFrom, string ValidTo)
{
  if (Codes.Count < 1 || String.IsNullOrEmpty(PONumber))
  {
    return false;
  }
  string sql = "INSERT INTO gift_codes (code, customerPO, validFrom, validTo) values (@code, @po, @from, @to)";
  string code = "";
  MySqlCommand cmd = new MySqlCommand(sql, Conn);
  cmd.Parameters.AddWithValue("@po", PONumber);
  cmd.Parameters.AddWithValue("@from", ValidFrom);
  cmd.Parameters.AddWithValue("@to", ValidTo);
  cmd.Parameters.AddWithValue("@code", code);
  cmd.Prepare();
  for (int i = 0; i < Codes.Count; i++)
  {
    code = Codes[i].ToString();
    cmd.ExecuteNonQuery();
  }
  return true;
}

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