Nintex Forms for Nintex Workflow

Is Nintex Forms for Nintex Workflow purchased separately?  I was looking through the licensing options but did not see it as something that would be added, however I was told that my 'Edit Task Form' is not working because Nintex Forms for Nintex Workflow was not purchased.  The button is enabled but when I click it and select Nintex Forms nothing happens.  Actually when I select InfoPath it also does nothing. The same thing happens for a start form.  Thanks for any insight.