How to reference project in Visual Studio?

My first project is a simple turn-based card game. I developed the logic for the game outside of Unity in Visual Studio. I now wish to incorporate it (Visual Studio project) into my Unity app. I cannot figure out how to reference the logic code in Visual Studio.

I added the project to my solution. Intellisense says that I need to add a reference to my project and offers to do so. I do this, but it doesn’t seem to do anything. Now Intellisense indicates that I just need to add ‘using MyLogic’. I did that but the compiler doesn’t recognize that namespace.

What am I missing?