Preview the ads you set up for your line items. This way, you can verify how the ad appears based on your settings. To help visualize the actual size of your ad, you can turn on or off the display of a red border around it. (By default, this red border does not display.) To turn on the display, check the box above the ad. In addition, you can refresh your ad preview without reloading the entire page; click Reload Preview.
To preview an ad:
Open the view ad screen for the ad that you want to preview.
Click the Ad Preview tab.