Can't install the SDK

When trying to install the package via nuget from VS 2019, I get this error: "Could not install package 'BlockIo 2.0.4'. You are trying to install this package into a project that targets '.NETFramework,Version=v4.7.1', but the package does not contain any assembly references or content files that are compatible with that framework. For more information, contact the package author."	
