Submit domain error with working subdomain

[latnino]

Hey guys, I have set up my domain with strato, changed the nameserver to cloudflare with a running ddns and with proxy disabled. I have forwarded the ports 433, 80, 8443 on my router and checked its working with an online tool. But somehow when I try to register my AIO instance by submitting my subdomain I get the following error:

The domain is not reachable on Port 443 from within this container. Have you opened port 443/tcp in your router/firewall? If yes is the problem most likely that the router or firewall forbids local access to your domain. You can work around that by setting up a local DNS-server.

But if I open my.subdomain.de:443 I can see the expected code

Any helps and tips are welcome

[szaimen]

So you tried to submit my.subdomain.de and it does show you this error?

[latnino]

the subdomain with the port is accessible from my phone over mobile data but inside my home network I cant reach the page with the subdomain, whereas with the IP:port it works

btw my subdomain is different but I think this doesn’t change anything
all ports are open and accessible

[latnino]

I have tried setting up a local dns server as recommended by the error message, but as of now it hasnt helped at all