How to provide access to a computer from the Internet on Keenetic III?

Question

ZyXEL

The computer has Redmine installed, available on a specific port, to which you need to provide access from the outside.
As an example, let it be 192.168.1.50:3500
In the network address translation (NAT) rules, I set:
Interface: Broadband connection (ISP)
Protocol: TCP
TCP / UDP ports: One port: 3500
Redirect to address: 192.168.1.50
New port number destination: 3500
After that I try to open it in the browser via external_ip:3500, but I get an error (Unable to access the site ...)
PS External IP, of course, is white.