inadyn

Logged in, the setup assistant fills in your own host name and token.

inadyn is a small DynDNS client for Linux and embedded devices (UniFi uses it, too).

Put this into /etc/inadyn.conf:

period = 300

custom dynr {
    username    = <your-host>.dynr.net
    password    = <your-token>
    ddns-server = dynr.net
    ddns-path   = "/nic/update?hostname=%h&myip=%i"
    hostname    = <your-host>.dynr.net
}

Then restart inadyn, e.g. sudo systemctl restart inadyn. %h becomes the host name and %i the current IP address.

Check

inadyn -1 --foreground -l debug runs one update and prints the answer.