What does BadImageException mean and how do I fix it?

Question

I have a project using .NET Core 2.1 SDK and I want to use a dll on my project.

The Dll use Pechkin.synchronized NuGet Package.

I referenced the dll my project create an instance and invoke a method I get BadImageException.

How can I use this dll? Pechkin.synchronized does not support .NET Core 2.1. Is there a way to use this dll on .net core project?