How to style a .NET library so that you can call it from C++?

Question

.NET

It has its own .NET library, which has interfaces, classes, and simple methods. From complex types, only decimal. In one more place, it is necessary for the client code to create a class that implements a certain interface and pass it back to the library as a parameter.
It is necessary to add to the library the ability to provide its functionality to C ++ code. I read it on Google - there are no simple solutions. Yes, and somewhere they recommend COM, where some other crutches are fenced. In general, I could not determine the best way. Who will advise what?
UPDATE:
As far as I know, COM requires a strong-named assembly. For me, this is not an option, since it is not possible to sign the assembly, for some reason.

Answer 1

There is not much text, so even if your English is not very good, you should understand.
www.codeproject.com/Tips/695387/Calling-Csharp-NET...

Answer 2

COM

Answer 3

If not COM, then rewrite everything in C++ :-)