Page Not Found

Hi,

I am in the process of setting up a forum on my site horsenetservices.com

I have this permalink:-

Permalink: https://horsenetservices.com/topic/horse-shows/ ?

Have hit publish but I receive a “Page Not Found” error.

I have hit the “Preview” button but alas the same result…

What have I done wrong?

Any advice most welcome.

Thanks Dotty