API Gateway with multiple instances of a same Web API

Like already mentioned by the comment thread, you can load your COM model in a single-thread appartment state. If it's a legacy COM component, you have two major options to achieve it: either via registry or via your code.

A. If the COM component is correctly deployed and registered, you can change the appartment state via the registry with ThreadingModel 'Apartment' being a single-thread apartment.

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID
   {CLSID}
      InprocServer32
         (Default) = path
         ThreadingModel = Apartment

B. The other way is programmatically instantiate the COM component in a single-thread apartment, which would look somehow like this in your code:

using System.Runtime.InteropServices;

// create a new thread in single-thread apartment state
var staThread = new Thread(LoadCOMComponent);
staThread.SetApartmentState(ApartmentState.STA); 
staThread.Start();
staThread.Join(); 

static void LoadCOMComponent()
{
    try
    {
        var comType = Type.GetTypeFromProgID("yourobject");
        // activate COM object
        var comObject = Activator.CreateInstance(comType);
        // use COM object
        [your code]
        // release COM object
        Marshal.ReleaseComObject(comObject);
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error: {ex.Message}");
    }
}