从Excel VBA RingCentral FaxoutAPI的HTTP发布

我需要帮助让这个代码工作。 我在VBA编程方面是全新的，以及任何与HTTP Post和表单有关的东西。 我试图通过在这里阅读问题并遵循API帮助来做所有事情，但似乎没有任何工作。

这里是你可以findAPI参考的网站： http : //service.ringcentral.com/faxoutapi/

另外这里是我到目前为止的代码：

Sub POST() Dim WinHttpReq As Object Set WinHttpReq = CreateObject("WinHttp.WinHttpRequest.5.1") Dim strURL As String Dim PostData As String strURL = "https://service.ringcentral.com/faxapi.asp" Const Boundary As String = "---------------------------7d54b1fee05aa" WinHttpReq.Open "POST", strURL, False WinHttpReq.setRequestHeader "Content-Type", "multipart/form-data; boundary=" & Boundary PostData = "--" & Boundary & vbCrLf PostData = PostData & "Content-Disposition: form-data; name=""Username""" & vbCrLf PostData = PostData & "username" & vbCrLf PostData = PostData & "--" & Boundary & vbCrLf PostData = PostData & "Content-Disposition: form-data; name=""Password""" & vbCrLf PostData = PostData & "password" & vbCrLf PostData = PostData & "--" & Boundary & vbCrLf PostData = PostData & "Content-Disposition: form-data; name=""Recipient""" & vbCrLf PostData = PostData & "faxnumber" & vbCrLf PostData = PostData & "--" & Boundary & vbCrLf PostData = PostData & "Content-Disposition: form-data; name=""Coverpagetext""" & vbCrLf PostData = PostData & "This is a test fax from web" & vbCrLf PostData = PostData & "--" & Boundary & vbCrLf WinHttpReq.Send (PostData) MsgBox WinHttpReq.ResponseText End Sub 

我不断得到5的响应值，这意味着一个通用的错误。 我很确定这个表格与正确的格式不符。 我也想能够上传一个文件，如API的参考资料所示。

提前致谢