Adding Blazor to an existing Razor Pages project

//...
services.AddRazorComponents().AddInteractiveServerComponents();
//...
app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();
app.UseBanMiddleware();
app.UseAntiforgery();
app.UseEndpoints(endpoints => {
    endpoints.MapRazorPages();
    endpoints.MapControllers();
    endpoints.MapOgma3Endpoints();
    endpoints.MapGroup("panel")
        .MapRazorComponents<App>()
        .AddInteractiveServerRenderMode();
});

An unhandled exception has occurred while executing the request.
System.InvalidOperationException: Unable to find the provided template 'panel/'