any hints as to why this throws a “configuration file was not found and is not optional” exception?

string relative_path = "../../../../appsettings_global.json";
if (File.Exists(relative_path)) {
   IConfigurationRoot global_config = new ConfigurationBuilder().AddJsonFile(relative_path, false, true).Build();
   global_settings = global_config.GetRequiredSection("Settings").Get<GLOBAL_SETTINGS>();
}