Okay. I made the restriction rule less restrictive. I removed the {HTTP_ACCEPT_LANGUAGE} condition (so that regardless of the language of the web browser, the same rule applies). At the same time, I shortened the regex model and additionally unchecked the “Ignore upper and lower case” box (to make it Case-Sensitive).
My rewrite rule looked like this:
Also very important: delete browser data (previous cookies and cache, etc). Even trying a private browser might help. And it worked!
Thank you very much for your help @orchal