Title

I am trying to invoke a method using RTTI calls but I been struggling to do so

Here is my sample code

{$RTTI METHODS([vcPublic, vcProtected, vcPrivate])}
TBill = class sealed
private
Procedure Extract ;
procedure Tansform
Procedure Load;
public
constructor create (aFlagDb : Boolean); overload;
Procedure InvokeMethod(aMethodName: string; const Args: array of TValue);
end

procedure InvokeMethod(aMethodName: string; const Args: array of TValue);
var
Method :TRttiMethod;
rtype :TRTTIType;
begin
rtype := TRTTIContext.Create.GetType('TBill');

Method := rtype.GetMethod('Extract'); -> Returns Nil why?
Method.Invoke(self, Args);

end

Any Ideas?