That is not true. You don't need conid to place an order.
?
For example, to place an order for the ES E-mini future for March 21, all you need is:
LocalSymbol = "ESH1"
SecType = "FUT"
Exchange = "GLOBEX"
Try it yourself!
If you expect multiple answers or wonder what should be specify, use reqMatchingSymbols(211, "xxxxxxx") quick and efficient.
That deliver immediately nearly all you need to prepare future request.
If you are an adept of guessing, set Exchange = SMART and Primary empty or "ISLAND" for Nasdaq, NYSE for Nyse etc ...
But unless misinterpreting your intention you will need "conid" anyway to pass an order and this one you cannot guess it.