NC AIO on Synology Docker Domainchecker - Port 443 not reachable

Hello together

When i try to do the AIO installation i get 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.

It happens if I try it over the internet and from inside the local network.

domaincheck:

Where is my mistake?

Regards