R httr curl 404错误

Question

如果我在终端中使用以下内容，则会收到回复

curl -XPOST 'https://api.wit.ai/converse?v=20170120&session_id=aqblurqqfb&q=Hi' \
  -H "Content-Type: application/json" \
  -H "Accept: application/json" \
  -H 'Authorization: Bearer U4FSEI23I742US2MONJML3UHL3DYC4XO'

但我正在使用httr包的GET（）函数编写等效的R代码

require(httr)
GET(url="https://api.wit.ai/converse?v=20170120&session_id=aqblurqqfb&q=Hi",
    add_headers("Content-Type"="application/json",Accept="application/json",
                 Authorization="Bearer U4FSEI23I742US2MONJML3UHL3DYC4XO"
               )
   )

但是当我在R中运行它时，上面得到了404响应。任何想法我在这里做错了什么？在此先感谢。