Good evenig,
I made the ddns setting after installing the needed package, I can see the noip pinging the pubblic ip address but whenever I try to access I get a Watchguard page with user id and password requesting.
It may be your Watchguard anti-virus is preventing you from initially accessing an unknown website without admin authentication. Since the IP provided through the ISP to the RUT device will be considered an unknown site, it will be considered unsafe by many anti-viruses initially.
I would contact your system administrator to ask them to white-list the current IP in order to test your remote connection through the domain provided by noip.com.
Generally speaking, without any anti-virus setup on your device you are using to browse, the noip domain name should allow you to access the login screen of the RUT device.
Especially if you are already able to confirm that noip can ping/see the given public ip address.