Cannot find method although defined and used?

namespace KupoFinder.AppConfigHandler;

public static class AppConfigHandler
{
    private const string ConfigFileName = "KupoFinder.settings.json";

    public static void CheckConfigFile(){}

    // ...
}

using CommunityToolkit.Mvvm.ComponentModel;
using KupoFinder.AppConfigHandler;

namespace KupoFinder.MVVM;

public partial class MainWindowVM : ObservableObject
{
    public MainWindowVM()
    {
        AppConfigHandler.CheckConfigFile();
    }
}