Consider using custom configuration instead of selecting dnsexit.com from the drop-down.
Use the following Update URL: http://api.dnsexit.com/dns/ud/?apikey=[PASSWORD]&host=[DOMAIN]&ip=[IP] - copy/paste it without changes.
While configuring from Luci, put your API KEY into password field and your FQDN into domain field. Put whatever you want into username field.
Install curl and hostip (or drill or another similar tool) and configure certificate path as /etc/ssl/certs/ca-certificates.crt, tick "Use HTTP Secure".
If the problem persists, show more lines of your log, see this example.
Leave the 1st octet of your IP address as it is and hide the rest if you wish.