使用RCurl从R调用Twilio API

Question

我正在尝试使用R通过Twilio发送短信。以下代码有效但发送短信后，它会尝试保留连接选项。

library(RCurl)
Twilio_Account_SID <- "YourKey"
Twilio_Account_TOKEN <- "YourToken"
Number_From <- "+44*********"
Number_To <- "+44*********"
the_url <- paste("https://api.twilio.com/2010-04-01/Accounts/",
                 Twilio_Account_SID,"/Messages.XML",sep="")
output <- postForm(the_url,
                   .opts = list(
                     userpwd = paste(Twilio_Account_SID,":",Twilio_Account_TOKEN,sep=""),
                     useragent = "RCurl",
                     verbose = TRUE
                   ),
                   .params = c(From = Number_From, 
                               To = Number_To, 
                               Body = "I am sending a test message" 
                   )
)

然后我收到这条消息：

< Connection: keep-alive
< 
* Connection #1 to host api.twilio.com left intact
Error: UNAUTHORIZED

你有什么想法解决这个问题吗？