为何显示Bad Gateway

[luckypoem]

hi.

在服务器上，
root@p1601860745:/fpage-project1# grep -rn 9000 .
./config.py:4:PORT = 9000
root@p1601860745:/fpage-project1# nano config.py
root@p1601860745:~/fpage-project1# python3 app.py
Server started at 127.0.0.1:9001

然后我在本地机器的浏览器里访问vps-public-ip:9001 ,显示Bad Gateway
怎么解决？