jacekJ-9

Problem:
I configure the language functionality on different domains on the website. I followed all the steps from: https://wpml.org/documentation/getting-started-guide/language-setup/language-url-options/how-to-use-wpml-with-different-domains-per-language/
After entering the second domain http://progressjaproject.eu
and saving, I get "Not valid". The second domain I am adding does not have an SSL certificate. Could this be a non-validation problem?

Solution:
Yes, in order to enable this language URL format, it's necessary that all domains have the SSL certificate. If you check the "What you will need" section on the documentation that you mentioned, you'll see that the last item is:

- You should have an SSL certificate for each site translation, or one multi-domain SSL certificate.

Please check it: https://wpml.org/documentation/getting-started-guide/language-setup/language-url-options/how-to-use-wpml-with-different-domains-per-language/#what-you-will-need

I'll also attach two past threads where the clients were not able to validate their domains due to this issue with the SSL certificate:

https://wpml.org/forums/topic/ali/
https://wpml.org/forums/topic/httpsssl-need-to-work-on-the-2-domains-linked-to-1-wordpress/

As soon as you enable the SSL, the second domain will work fine. Please review this option with your hosting provider and let us know how it goes.