using wp mu 2.8.6 – can't find checkbox after activation

I installed the plugin, activated it, then went to create a new post, but I’m not seeing the checkbox. I logged out, logged back in, still didn’t see it. So I deactivated it, then activated it sitewide, still couldn’t see the checkbox.

My new/edit post screen is different from the one in your screenshot. Is the checkbox supposed to be in the publish area where you see drafts, visibility, schedule etc?

https://www.ads-software.com/extend/plugins/secret-content/