Can't access password protected page

I set up a password-protected page in order to run a test, however when I try to access the page I get a 404 “page does not exist” message, instead of a “please insert your password” message.

I have read all the instructions for setting up such a page and have clicked “publish” after setting the password.

The page link is: https://supernutrientsdiet.com/ebook/supernutrients-diet-3/