Avanti and AvantiFlex configurations require a license key and license units to run.  At the bottom of each virtual Alpha configuration window, the total number of license units required is displayed.  Clicking the [show units] button provides a detailed list of the license units required.

The image above depicts an Avanti configuration that requires 115 license units.  Note the summary of required license units at the bottom of the configuration window.  Clicking the [show units] button displays the License Unit Calculation box which details the required license units.