This means that your submitted campaign did not seem to have any campaign items in it.

Creating a campaign does not mean that there is content in it to run. In order for a campaign to run on the Taboola network, it must contain at least one campaign item. Each item should have a title, thumbnail and a destination URL. 

How To Fix
​Make sure to submit campaign items to your campaign.
When setting up a new campaign, make sure to add campaign items to the campaign inventory before submitting. Each campaign item should have a title, thumbnail image or video creative, and destination URL.

To learn how to fix and resubmit your campaign or campaign item, click here.