It is difficult for us to troubleshoot the problem since we can't verify there is an issue on our end. And, we don't understand the complete steps you're taking to post a review. There's not more we can do but see if there's a problem with your web browser, computer or account. I can see from my end that you haven't created a profile to post reviews on Google Maps. That's likely an issue when you're trying to post a review. You must sign in with this account to post a review.
Before writing your review, please try clicking the Sign in button, just above the Owner-verified message.