DDNS Custom URL failing

Hi guys,

I'm wondering if you can point me in the right direction. I've had DDNS working for months, but since about April, the TomatoUSB update has been failing to update the DNS (I'm using nsupdate.info).

URL code I've been using is the following (username/password changed):
https://myname.nsupdate.info:xxxxxxxxx@ipv4.nsupdate.info/nic/update

If I paste the code into the url bar of a browser, nsupdate.info updates DNS smoothly, but tomato seems to be failing for some reason....

DDNS Custom URL failing