Heroku为网络挂钩事件引发错误H26错误标头

Question

我有一个第三方服务，该服务将Web挂钩事件发送到部署在Heroku中的NodeJS应用程序。但是Heroku阻止了此服务发送的请求，并显示以下错误

 cause="bad header"
 at=error code=H26
 desc="Request Error"
 method=POST
 path= "<web hook receiving endpoint>" 
 host=<heroku app url>
 request_id=<heroku request id>
 fwd="<ip>"
 dyno= connect= service= status=400 bytes= protocol=https

我尝试将带有Ngrok的webhook转发到我的本地计算机，所有标头似乎都很好。

"{
   "accept-language": "en-US,en;q=0.9",
   "accept-encoding": "gzip, deflate, br",
   "referer": "<Web hook sender>",
   "content-type": "application/json;charset=UTF-8",
   "dnt": "1",
   "user-agent": "my ua",
   "origin": "<Web hook sender>",
   "accept": "application/json, text/plain, */*",
   "content-length": "247",
   "host": "<ngrok id>.ngrok.io",
   "connection": "upgrade",
   "x-forwarded-for": "<ip address>"
}

为什么heroku会为此请求引发错误？