[Resolved] We want the german language to be connecte via "de" domain

Problem:
In some cases WPML will print the "not valid" error when saving the URL format for different domains per language inside WPML > Settings > Language URL Format.

Even though, the DNS config is correct and the domain is working, it might be that WPML is unable to validate it.

Solution:
In some cases, disabling "Validate on save" checkbox before clicking the Save button can solve such issues.

Take note, that if this will not solve the issue, then it is more likely that the DNS setup is not correct and you should consult your hosting support team.

Relevant Documentation:
https://wpml.org/documentation/getting-started-guide/language-setup/language-url-options/how-to-use-wpml-with-different-domains-per-language/