我无法通过vb.net中的Amazon SNS向移动设备发送消息

Question

我想通过Amazon SNS向用户发送短信。我在vb.net中编写了以下代码，但发生了错误：

  

“消息属性'AWS.SNS.SMS.SMSType'具有无效的消息属性类型，支持的类型前缀集为Binary，Number和String。”

我的按钮单击事件代码是：

 Imports Amazon.SimpleNotificationService
 Imports Amazon.SimpleNotificationService.Model

 Public Class Form1
     Dim myclient As New AmazonSimpleNotificationServiceClient

     Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim snsreq As New PublishRequest
        Dim snsres As New PublishResponse
        Dim snsmsgstng As New Dictionary(Of String, MessageAttributeValue)()
        snsmsgstng.Add("AWS.SNS.SMS.SenderID", New MessageAttributeValue() With {.StringValue = "testing", .DataType = "string"})
        snsmsgstng.Add("AWS.SNS.SMS.SMSType", New MessageAttributeValue() With {.StringValue = "Promotional", .DataType = "string"})
        snsreq.MessageAttributes = snsmsgstng
        snsreq.PhoneNumber = "+972543784512"     'phone No
        snsreq.Message = "you get message ,if yes then tells me???.."
        snsres = myclient.Publish(snsreq)
     End Sub
End Class

然后在app.config文件中添加以下代码

<appSettings  >
  <add key="AWSAccessKey" value="MYAWSAccessKey" />
  <add key="AWSSecretKey" value="MYAWSSecretKey"/>
  <add key="AWSRegion" value="ap-southeast-1"/>
</appSettings>

我不知道代码在哪里。