ETABS OAPI : CreateObject method not found on Helper Class using C#

Question

newbee here

I am trying to work with ETABS OAPI (structural engineering software) using C# and start with the example on its documentation.

//declare etabs object
ETABSv17.cOAPI myETABSObject = null;

//Use ret to check if functions return successfully (ret = 0) or fail (ret = nonzero) 
int ret = 0;

//create API helper object
ETABSv17.cHelper myHelper;

myHelper = new ETABSv17.Helper();

  
//create ETABS object
try
{
    myETABSObject = myHelper.CreateObject(programPath); //PROBLEM IS HERE
}
catch (Exception ex) { Console.WriteLine("Error : " + ex); }

The error said:

System.MissingMethodException: Method not found: 'System.Object System.Activator.GetObject(System.Type, System.String)'.
   at ETABSv17.Helper.StartNET(String fullPath)
   at ETABSv17.Helper.CreateObject(String fullPath) in ETABSv17.dll:token 0x600011e+0x12
   at <Program>$.<Main>$(String[] args) in C:\Users\edithb\source\repos\ConsoleApp1\ConsoleApp1\Program.cs:line 38

Looks like the method CreateObject has not been defined yet inside Helper Class. But it should work since it written on example of its documentation. please help or recommend other way to make it work. Thanks