Ngrok错误'502 bad gateway'。

我对使用任何网络应用程序都很陌生，最近一直在尝试缓慢地构建一个Facebook Messenger机器人。但是当我尝试使用ngrok时，我无法访问给定的地址，例如：

ngrok http 5000

我在命令行中输入的是这样的，它返回了如下结果：

ngrok by @inconshreveable

Session Status                online
Version                       2.1.18
Region                        United States (us)
Web Interface                 http://127.0.0.1:4040
Forwarding                    http://ea986ca5.ngrok.io -> localhost:5000
Forwarding                    https://ea986ca5.ngrok.io -> localhost:5000

Connections                   ttl     opn     rt1     rt5     p50     p90
                              0       0       0.00    0.00    0.00    0.00

但当我按照Facebook开发者页面所要求的方式使用地址 'https://ea986ca5.ngrok.io' 时，它显示：

The connection to http://ea986ca5.ngrok.io was successfully tunneled to your
ngrok client, but the client failed to establish a connection to the local  
address localhost:5000.


Make sure that a web service is running on localhost:5000 and that it is a 
valid address.


The error encountered was: dial tcp [::1]:5000: connectex: No connection 
could be made because the target machine actively refused it.

我的本地端口有问题吗？谢谢！