Consuming idispatch COM component in C#

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C++

C#

COM

I have written a COM component in C++ (6.0 - I know its old but I'm learning using it) using the IDispatch interface and am trying to consume it in C#.

My C# code is as follows:

static void Main(string[] args)
    {
        Type type = Type.GetTypeFromProgID("Bens.General.1");
            
        Object obj = Activator.CreateInstance(type);

        ITest tObj = (ITest)obj;
            
        Console.WriteLine("Value1: " + tObj.MyValue());

        Console.ReadLine();
    }

(I have also tried this using dynamic but no luck there either).

with the following ITest interface:

[Guid("4B8C6960-EB25-11e7-A3BD-001CF0FAD303")] // This matches my IID in Component QueryInterface

    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface ITest
    {
        [DispId(1)]
        string MyValue();

        [DispId(2)]
        string Value2();
    }

The C++ QueryInterface is:

HRESULT __stdcall Cmpnt::QueryInterface(const IID& iid, void** ppv)
{
	char buffer[37];

	char* guid = guid_to_str(&iid, buffer);

	MessageBox(NULL, guid, guid, 0);

	if(iid == IID_IUnknown)
	{
		*ppv = static_cast<general*>(this);
	}
	else if(iid == IID_IDispatch)
	{
		*ppv = static_cast<general*>(this);
	}
	else if(iid == IID_general)
	{
		*ppv = static_cast<general*>(this);
	}
	else
	{
		*ppv = NULL;
		return E_NOINTERFACE;
	}
	
	reinterpret_cast<IUnknown*>(*ppv)->AddRef();

	return S_OK;
}

IID_general definitely matches the GUID in the ITest attribute.

What I have tried:

It works fine in VB6 and VBA (Office 2016) but in C# says that the Interface
{

4B8C6960-EB25-11e7-A3BD-001CF0FAD303

}
Isn't implemented but I know for a fact that in the C++ QueryInterface method it is (it works in VB/VBA so why not C#?)

The MessageBox in the C++ code shows the C# is trying at least 10 IID's including the IID_general which seems strange to me with no luck. VBA, Excel shows that it tries 6 IID's and succeeds after that.

UPDATE: I have updates my COM component to support early binding with type library, MIDL generated interfaces, etc... - again this works for VBA (Excel) but not in C#.