CSharp SDK dbx.Files.UploadAsync doesn't work

Hi Steve, thanks for your tip, I've tried the forward slash but it doesn't work.

The primary call is essentially straight from the CSharp SDK, which is:

using (var dbx = new DropboxClient("My_Key"))

{

    await UploadToDropBox(dbx, "/test", "test.txt", "Hello Dropbox"); // tried with /test and just test

}

And the method it calls (exactly from the SDK with a Console.WriteLine(...) removed: 

async Task Upload(DropboxClient dbx, string folder, string file, string content)
{
    using (var mem = new MemoryStream(Encoding.UTF8.GetBytes(content)))
    {
        var updated = await dbx.Files.UploadAsync(
            folder + "/" + file,
            WriteMode.Overwrite.Instance,
            body: mem);
    }
}

But, as stated, without results.

Kind regards,

Anthony