No connection string named 'BACEntities' could be found in the application config file.” when calling 'n .NET Framwork 4.7.2 Library from .NET 5 Api

Question

I have a .Net 5 API and would like to use my .NET Framwork 4.7.2 Library that has access to my Database. However, I get the error “No connection string named \'BACEntities\' cou