FritzBox not updating, manually calling URL works

[Schuasda]

I have gone through the instructions and the cloudflare and FritzBox documentations multiple times, but can't find my error.

My setup:

• Some old PC with ubuntu as server in my home network

• A FritzBox 7590 as my network router

• This project deployed as a docker container on said server

• Cloudflare account, where i registered my domain and route it to the public IP of my FritzBox

This works. I have configured my FritzBox with this:

where "schubuntu" is the hostname of the server and the password is an API token from cloudflare. The full URL is this:
http://schubuntu:9017?token=<pass>&zone=<domain>&ipv4=<ipaddr>&ipv6=<ip6addr>

Now the issue: I had multiple changes of my public IP over the last little while, but my DNS records where never updated.
When i manually enter the update-url in a browser and replace pass, domain, ipv4 and ipv6 I get a success response and the record is updated. So my guess is that the router just doesn't call the URL or replaces wrong parameters?

Please tell me what i did wrong or if the FritzBox not working correctly.

Any help is appreciated, thank you
Simon

[L480]

Could you please check the FritzBox logs? Have you tried using the IP address of schubuntu oder at least the FQDN (schubuntu.fritz.box) for the Update-URL?

[Schuasda]

I did check the logs, but weirdly there was no mention of anything about DynDNS at all. Unless there is some other secret log, the System > Event Log never mentions DNS in the connection or system category.
I changed the host to the actual IP now, triggered a reconnection through the FritzBox but it still did not update the record at cloudflare :(
Also: I can enter either the hostname or the IP of my local server in my browser and go to the update URL and it works, so I really feel the issue is in the FritzBox.

So at this point, do you think I should rather reach out to AVM support?