C# GetResponseAsync() : How to use correctly

I'm developing an application using the Twitch API, and I tried to use asynchronous request.

I test before with a synchronous request, like this :

private async static Task<string> generalRequest(string url, string method, object payload = null, string accessToken = null, API api = API.V5, string clientId = null)
{
    url = appendClientId(url, ClientId);

    var request = WebRequest.CreateHttp(url);
    request.Method = method;
    request.ContentType = "application/json";
   
    var response = request.GetResponse();
    using (var reader = new StreamReader(response.GetResponseStream()))
    {
        string data = await reader.ReadToEndAsync();
        return data;
    }
}

It works great but this is not asynchronous.

I tried with GetResponseAsync() like this :

using (var response2 = await request.GetResponseAsync())
{
    using (var reader = new StreamReader(response2.GetResponseStream()))
    {
        string data = await reader.ReadToEndAsync();
        return data;
    }
}

However, it never got through the first using, and I got these exceptions :

Exception levée : 'System.Net.WebException' in mscorlib.dll

Exception levée : 'System.Exception' in LivestreamerTwitchViewer.exe

Exception levée : 'System.Exception' in mscorlib.dll

So what I did wrong?

How do I use GetResponseAsync() correctly?

Thanks in advance for your help.