Support › General › Licencing
Please where to put licence key to activate licence ?
Please go to Admin Dashboard > Meta Box > License > Add the license key to the box and click Save changes to activate the Meta Box license on your site.
I don't have meta box in main menu, only in installed plugins
The Meta Box menu appears only when you have at least one premium extension. If you don't have any premium extension, it won't show in WordPress (in that case, you don't need license key).