According to ThemeForest terms, the main difference is that under the Regular License, your end product (incorporating the purchased item) is distributed for free, whereas under the Extended License your end product may be sold or accessed by paying users. In both cases, the licensing is relative to one website (or client project).
In summary, our understanding is that you can either:
– Buy a new license for each new client project as long as the built online service is not sold to end users, or
– Buy a new extended license for each new client project if the built online service is accessed by end users in exchange for a fee.
You're trying to setup your theme but you're experiencing errors when importing the demo content? Or you've just followed the setup guide but your website doesn't look exactly like our demo? These are common issues for which you can find easy and quick fixes.