I'm stuck, as with others here, on not being able to post comments?
I've got the REST UI installed and configured (with cookie auth) for all the React Comments enabled (GET/PUT etc).
I don't know why, but /rest/session/token is not available (404) according to a console error, and it put up an error in the UI saying "e.response is undefined". Makes me think it can't find a token to authenticate with? So I added an alias to point it instead at /session/token which does return a value. I've seen /rest/session/token referred to in docs and other places, so not sure if something changed in D9 where that pathway has been deprecated?
With the redirect alias in place, now it reports a different error saying "No route found for "POST /react-comments/comments/1170": Method Not Allowed (Allow: GET, HEAD)". If I just put in that URL, it works (returns data) so not sure why the route isn't found, nor why it doesn't have POST permission when the Rest UI says it does?
Drupal 9, PHP 7.4, no watchdog errors related to this at all, so not sure what else to offer up to help with troubleshooting? If I fiddle with the Rest UI settings or the Drupal permissions the changes are having an impact. For example, removing GET access from Anonymous means that existing comments (entered in Drupal before React Comments) are not shown. So it seems all the pieces are working somehow, but not being able to post new comments makes this a little problematic.