I took a look and the minimum requirement to be able to post within the Classifieds is 10 posts, which you guys have well over that amount. Do you get an error message when you attempt to post in the Classifieds? Is it only this section that you're unable to post or you have the same issue in other sections as well? What device/browser are you using? Have you tried a different device/browser to see if the problem persists? Try clearing your cache/cookies and see if that maybe helps?
I hope one of these help. Let us know if you need further assistance.