Sorry but I’ve missed a step of this page viewtopic.php?p=22271#p22271. I missed step 4 to install the no-ip software.
Now everything it’s working.
Thanks again for the support.
We don’t offer dedicated NoIP software anymore. This is now fully integrated into dietpi-ddns
yes ok. But I’ve inserted my no-ip credential and ddns domain in dietpi-config → network options → dynamic DNS.
Now it’s working in and outside of the network 
that’s the long way. Shortcut would be dietpi-ddns