PayPal Get Access Token vb.net请求被中止：无法创建SSL/TLS安全通道

关于调用PayPal的授权访问令牌API，我有几个问题，下面是我的代码：

Public Function testAPI() As String
    Dim data As StringBuilder
    Dim byteData() As Byte
    Dim request As HttpWebRequest
    Dim response As HttpWebResponse = Nothing
    Dim postStream As Stream = Nothing
    Dim reader As StreamReader
    Dim Result As String = ""
    request = DirectCast(WebRequest.Create("https://api.sandbox.paypal.com/v1/oauth2/token"), HttpWebRequest)
    request.Headers.Add("Username", "XXXXXXXXXX")
    request.Headers.Add("Password", "XXXXXXXXXX")
    data = New StringBuilder("{""grant_type"":""client_credentials""}")
    request.ContentType = "application/x-www-form-urlencoded"
    request.Method = WebRequestMethods.Http.Post
    byteData = UTF8Encoding.UTF8.GetBytes(data.ToString())
    request.ContentLength = byteData.Length
    postStream = request.GetRequestStream()
    postStream.Write(byteData, 0, byteData.Length)
    If Not postStream Is Nothing Then postStream.Close()
    response = DirectCast(request.GetResponse(), HttpWebResponse)
    reader = New StreamReader(response.GetResponseStream())
    Result = reader.ReadToEnd().ToString
    Return Result
End Function

我是否以正确的方式传递用户名和密码

我是否以正确的方式传递“授权类型”：“客户端凭据”

我不断收到错误：请求被中止：无法创建SSL/TLS安全通道。我尝试添加一些从谷歌搜索的代码：

ServicePointManager.Expect100Continue = True
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
request.ProtocolVersion = HttpVersion.Version11

---

但它仍然失败并返回相同的错误消息。请帮助。

我不熟悉PayPal API，但只是尝试一下，如果您这样做会发生什么：

ServicePointManager.SecurityProtocol=SecurityProtocolType.Tls或SecurityProtocolType.Tls11或SecurityProtocolType.Tls12

？另外，我假设您在调用

WebRequest.Create（）

之前设置了这些值？如果仍然不起作用，您可能还想尝试在他们的问题追踪器上发布：哦，是的！非常感谢。我没有将这些代码放在WebRequest.Create之前。但现在我遇到了另一个错误，即401未经授权，因此我认为我的用户名和密码或授权类型没有正确通过。