Go to My TER and the box that says My Message Boards - click on that and it will show all the posts you've made recently and will say if they are active, new (waiting approval) or rejected.  If they were rejected it should state why it was rejected.

When I was a mod, I would often have to disapprove ads for various violations.  The most common thing was touring providers not putting the dates of their visit in the subject line.  If the ad you are trying to post is for you in a city other than your home base, that is the most likely reason for not allowing the ad to post.
You can go to your account manager and look at your posts.  If an ad post was denied, there should be a reason given there.  If it's not, you need to contact admin.

Good luck,
Swim