How to use this script?
Why, that's simple! Copy this script to your USG, run chmod +x on it and then, as a user with sudo permission, execute it.
Shamelessly borrowed from Brittanic on the Ubiquiti Unifi forums
How to use it?
Simply run the following command (note, if you are at all security concious-don't run it and instead review the script, then copy it to your USG to execute).
curl https://gist.githubusercontent.com/troyfontaine/7e6f93e32621177fc9a94e823adc52b5/raw/fix_ddns.sh | sudo bash
But I don't see Cloudflare in the Unifi Controller!
Well you won't? This updates the client-so you still need to use the config file method of telling the USG to use ddclient to talk to Cloudflare.
Why do I need it smart guy?
If you haven't heard, Cloudflare deprecated their older API in favor of their newer-so the old ddclient still included in the Unifi line of routers can't talk to it anymore.
For those of us who use Cloudflare for DDNS-it kinda sucked. This helped.