Discourseフォーラムへのアクセスを、会費の支払いを停止したユーザーに対してどのように制限できますか?

I am assuming you are using the WP Discourse plugin. There is nothing built into the plugin to handle this, but it can be done by adding some code to your site. Have a look at this post: How to prevent some WP users from being able to login to Discourse - #2 by simon.