Autofac can't find constructor in a Xamarin app, even it's there

Question

I'm trying to use Autofac to register a service into Xamarin.Forms (netstandard2.0)

here's my code:

SqliteManager.cs

public interface ISqliteManager
{
    void test();
}

public class SqliteManager : ISqliteManager
{
    private readonly string _path;
    public SqliteManager()
    {
        _path = "test";
    }

    public void test()
    {
        Console.Write(_path);
    }
}

App.xaml.cs

public partial class App : Application
{
    public App()
    {
        InitializeComponent();

        ViewModelLocator.RegisterDependencies();
        ViewModelLocator.Resolve<ISqliteManager>().test();
    }
}

ViewModelLocator.cs

public static class ViewModelLocator
{
    private static IContainer _container;

    public static void RegisterDependencies()
    {
        var builder = new ContainerBuilder();

        builder.RegisterType<SqliteManager>().As<ISqliteManager>().SingleInstance();

        _container?.Dispose();
        _container = builder.Build();
    }

    public static T Resolve<T>()
    {
        return _container.Resolve<T>();
    }
}

it's seems ok, but i get this error when i try to resolve the service in app.xaml.cs:

Registration: Activator = SqliteManager (ReflectionActivator), Services = [Tracker.Managers.Interfaces.ISqliteManager], Lifetime = Autofac.Core.Lifetime.RootScopeLifetime, Sharing = Shared, Ownership = OwnedByLifetimeScope ---> No constructors on type 'Tracker.Managers.SqliteManager' can be found with the constructor finder 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder'.

but sqlitemanager has a constructor!