пример работает

Example.Backend/Printer.cs

@@ -12,7 +12,7 @@ public class Printer : IPrinter
         return Name;
     }
 
-    public async Task<TransmittedSharedObject<IPage>> Print(string text)
+    public async Task<TransmittedSharedObject<IPage>> Print(string text, CancellationToken cancellationToken = default)
     {
         return new Page {Text = text};
     }

Example.Backend/PrinterFactory.cs

@@ -9,6 +9,6 @@ public class PrinterFactory : IPrinterFactory
 {
     public TransmittedSharedObject<IPrinter> Create(string printerName)
     {
-        return new Printer(){Name = printerName};
+        return new Printer {Name = printerName};
     }
 }