How to configure UCS 4 for external access

Hi,
I need some advise how to configure UCS4 for external access and mobile app/desktop app access.
EG: I setup on no-ip hostname nexcloudtest.ddns.net point to static WAN IP
I can login the website from external through https://nexcloudtest.ddns.net
But after successfully login, got direct to differrent link eg: servername.localdomain.local/nextcloud
Don’t know how to go about fix the issue, new to UCS4 and nextcloud.
Thanks in advanced