For anyone using a FritzBox, I seem to have successfully configured mine to update using the following details and the update URL exactly as entered:
DynDNS Provider: User-defined
Update URL: https://<user>:<pass>@api.cp.zoneedit.com/dyn/generic.php?hostname=<domain>&myip=<ipaddr>
Domain Name: *put your domain to be updated here*
User Name: *put your user name here*
Password: *put your token here*
DynDNS Provider: User-defined
Update URL: https://<user>:<pass>@api.cp.zoneedit.com/dyn/generic.php?hostname=<domain>&myip=<ipaddr>
Domain Name: *put your domain to be updated here*
User Name: *put your user name here*
Password: *put your token here*