Programatically control application auto start C/C++

I have a desktop bridge app. Using the app manifest, I can force my app to start at login time.

However, I want to programmatically enable/disable this feature, but I have not managed to do it yet.

#include <winrt/Windows.ApplicationModel.h>

using namespace winrt;
using namespace Windows::Foundation;
using namespace Windows::UI;
using namespace Windows::UI::ViewManagement;
using namespace Windows::ApplicationModel;

bool CppWinrt::makeStartup(int clear0Set1Query2)
{
    try
    {
        StartupTask startupTask = winrt::Windows::ApplicationModel::StartupTask::GetAsync(L"MyStartupId").GetResults(); // L"AD2F1837.HPAccessoryCenter").GetResults();
        if (clear0Set1Query2 == 1) startupTask.RequestEnableAsync().GetResults();
        if (clear0Set1Query2 == 0) startupTask.Disable();
        return startupTask.State() == winrt::Windows::ApplicationModel::StartupTaskState::Enabled;
    }
    catch (...) { return false;  }
}

Here is the stuff in the app package...

    <Extensions>
    <desktop:Extension
      Category="windows.startupTask"
      Executable="HPAccessoryCenter\HPAccessoryCenter.exe"
      EntryPoint="Windows.FullTrustApplication">
      <desktop:StartupTask
        TaskId="MyStartupId"
        Enabled="true"
        DisplayName="HPAccessoryCenter" />
    </desktop:Extension>
    </Extensions>

It compiles, but generates a run time error of: Exception thrown at 0x00007FFEFF7FA839 (KernelBase.dll) in HPAccessoryCenter.exe: WinRT originate error - 0x80070490 : 'Element not found.'.

Thanks, Cyrille