You can check your message boards by click on "My TER" at the top, and look to the left section of "My Quick Links", and click on "My message boards". There, it will show you the history of all your post, including your ad post. If your ad post was denied, it will provide you a reason why it was denied.

If you feel that you the message board was incorrectly denied, then click on "contact us" in the same denied post and explained your reasons.

"My board posts"