Hello.
If you want to create your site using our theme on the staging site first and then move on to the final domain, you can do it using a single license but for that, you have to unregister the license first from the staging site and then you will be able to activate the theme again on a final domain.
Please refer to our theme documentation here: https://www.portotheme.com/wordpress/porto/documentation/how-to-register-porto/
Best Regards.