I'm using paper trading for IB and try to add a future like this

AddFuture("HG", Resolution.Second);

I met below error

ERROR:: Brokerage.OnMessage(): Error - Code: 321 - Error validating request.-'bX' : cause - Please enter a valid security type. Origin: [Id=5] Subscribe: HG29Z21 (FUT HG USD NYMEX   0 )

I tried different symbol, but not worked.

:(