Dynamic DNS: Where can I find the logs for it? Trigger a push to update?

My domain registar/hoster do.de says in their guide for Unifi/inadyn based services to access their FlexDNS to select DynDNS in Unifi and enter the credentials, hostname and update-string.
Done that, but nothing happens on their end in terms of that the subdomain still holds 0.0.0.0 as the redirect-ip.

The unifi help docs say it will be run automatically. But nothing happens.
Where do I find the logs, to check if my UDR7 even tried to publish my IP to that FlexDNS system?

It worked really fine with my previous Fritzbox to update their FlexDNS system accordingly.