Thank you for your answer. Nope, no specific settings. Just romanian locals, preferences (single page checkout, quick order activated), SSL activated, php 8.0, the rest are defaults. If you try on domain arts-online.ro pick a product, try checkout with quick order, write some data ( romanian zip code is six digits like 442266) try to save and there is.
After some digging it looks like the problem arises al line 226 at OrderOpcController.php, but no php error was logged, as I was capable to find
If you like I can sent you the credentials to have a look at backoffice, anyway this domain is just for test
Thank you for help and advice
Horia