google drive upload multipart出错

我想把一个有元数据的文件上传到谷歌硬盘

以下是我的基本代码:

Sub DriveMultiUpload(Bytes As Byte(), Name As String)
        SetAuthHeaders("https://www.googleapis.com/auth/drive")
        Dim mp = New MultipartFormDataContent
        mp.Add(New StringContent(Name), "name")
        mp.Add(New ByteArrayContent(Bytes))
        Dim pb = mp.ReadAsByteArrayAsync.Result
        Headers("Content-Type") = "multipart/related"
        Dim response As Byte()
        Dim ret = New WebInfo(Of String)
        Try
            response = UploadData("https://www.googleapis.com/upload/drive/v3/files?uploadType=multipart", "POST", pb)
        Catch ex As WebException
            If ex.Response IsNot Nothing Then ret.Result = New StreamReader(ex.Response.GetResponseStream).ReadToEnd
        End Try
    End Sub

内容类型错误。请使用多部分。

[顺便说一句,我试过在Fiddler中调试,但是

1. 这个请求没有出现,
2. 当Fiddler打开时,响应是空的]

但我发现奇怪的是,一旦uploaddata返回,标头就不再包含任何内容类型,所以这可能是问题所在?

请告知