Ok, so I’ve just joined it. You have to search for it in the ‘All’ communities tab and subscribe there first. Then you can post. That advice you followed in the thread you linked to is wrong - they missed out a crucial step.

Thanks, that worked. I had found it once but it had an error while I was trying to post my comment.

Is there a better way than a title search? Right now that works but when there’s lots of activity it won’t be ideal. It would be nice to be able to put a URL into the search bar.