DynDNS update via URL ddclient

[sid112]

Hi All,
I'm starting to despair... I'm trying to transfer my IP to the DynDNS using ddclient (1.21_2) via Custom GET.
This is my server address: https://geraeteportal.gira.de/hsdyndns.php?u=USER&p=PASS&ip=%IP%

Unfortunately the placeholder %IP% is not exchanged for the IP address... is there perhaps another placeholder? Or can I add the IP to the ddclient.json?

I am thankfull for every opinion!

Thanks + greetings
sid