DNS entry to IP and Port?

In case the DNS provider failing, I would like to have a DNS entry or route on my Unifi Cloud Gateway to my selfhosted reverse proxy (Nginx on 172.16.10.30:7777). Therefore, I can still reach my applications using the domain.
I did create a DNS entry (Settings > Policy Table > DNS). However, I am note able to point it to the port 7777.

TLDR:
one.mydomain.com should be redirected to 172.16.10.30:7777
How can I achieve this with the Unifi Cloud Gateway?