Hi there,
Would you give a bit more clarification of the issue? What notification you got and which license you are referring? Visual Composer is an Integrated Plugin of X. You don’t need to activate it to use with X and there is no license key provided for integrated plugins. However if you want the premium features (support from WPBakery) then you need to purchase a separate license from CodeCanyon.
Make sure to use the compatible version installing from X Addons menu.
Cheers!