Could you ask your friend what exactly happened when he tried? To begin with, does your friend have an Itch.io account? Was he logged in? Otherwise it's not possible to leave a rating.
He was logged in and he said that he could not find the rate button (The rate option is enabled)
That's odd, I can see it just fine where it's supposed to be, in the upper right corner of the page. Not sure what could be causing the problem.
