.NET runtime licensing is used if .NET Framework runtime licensing is not (see .NET Framework Runtime Licensing). If you are transitioning a project away from the legacy licenses.licx technique, but targeting Dart .NET Framework assemblies; remove the licenses.licx file from the project OR the Dart component entries from the licenses.licx file.
How to use .NET Runtime Licensing:
Note: If your application creates instances of Dart components in separate application domains, a call to License.Set will need to be added to your code where it will be executed within the application domain itself.