If you look in your account stats, is the hub listed with a little swirly arrow icon? If so, that means it's in the pending stage during which ads are disabled for ~24 hours. When it clears that process, the ads will appear. It's all automatic, so there's nothing else you can do but wait unfortunately.
If the issue has persisted for more than a day you can also email the staff. They are usually pretty good about getting back to people. Good luck.