Missing Class Attributes

I'm trying to integrate Normcore into my Unity driving game. I followed the steps to create a MyCarModel class and added the [RealtimeModel] attribute. However, I'm not seeing the "Generate Realtime Model" option when I right-click on the MyCarModel.cs file. When I try to manually use the model, I get the error: 'MyCarModel' is missing the class attribute 'ExtensionOfNativeClass'.