Ad tag waterfall allows you to set several ad tags to a single ad break and the player will play the first ad that returns a valid response. When you create an ad tag waterfall, you assign an array of ad tags to a single ad break.
Player example above makes use of 3 ad tags. First ad tag is VAST xml without ad defined, the second ad tag is an empty XML file, finally third ad tag is valid VAST xml with an ad pod of 2 pre-roll ads. In browser's console you can see 2 errors in the attempt of loading 2 invalid ad tags.
The VAST PRO plugin is a separate product for Nuevo software version minimum 10.0 licence holders. Lifetime license per domain can be ordered upon first order, or any time later in client area. Nuevo software GOLD plan users are entitled to an almost 40% discount off the basic price.