Error404 in comments

Hello, my domain looks like https://mydomain.com and I try to resite from wordpress using Options / General / re-site the place to https://www.mydomain.com. The problem is that when I add the “www”, users can’t add comments. When they try to send the comment, an error404 prevents it. How can I fix this? My intention is that my domain has the “www” and no error when commenting. Thank you very much.