Hi @lucabuka,
and welcome to the forum.
What is the IP of the host in your Checkmk Server?
Is it 192.168.1.110 or the public IP of your Router/Firewall?
The registration worked because it’s the other way around. Your monitored host makes a HTTP/HTTPS request to the public Checkmk Server. TLS Registration normally uses Port 8000.
Another question is: Can you share a screenshot of your NAT rule on your firewall? I think there lies the problem. Another approach would be to packet capture the connection.
Regards
Norm