I was trying to setup ddns on my router but mine asks me for a port number. Which is your tutorials didn't mention about it. What port should I use? I tried couple ports but my dynamic ip didn't refreshed. Maybe the problem is not the ports, other values could be wrong. I attached a screenshot of my router configuration. I'll be glad if you can help me, thanks...

The server URL should be the below:

api.dynu.com/nic/update?username=[USERNAME]&password=[PASSWORD]