checkip.dyndns.org service returns LAN IP

Question

I using http://checkip.dyndns.org service to get external IP of users that uses my desktop app. (Found this here https://stackoverflow.com/a/20029996/5536881)

But sometimes for some users it returns local IP e.g. 192.168.0.141.

Is it possible to resolve this problem? And what can cause this?

Answer 1

The reason is that checkip.dyndns.org uses "X-Forwarded-For" header to return IP.

I try another sevice (https://ipecho.net/plain) and solve problem