All Divi Booster plugins (Divi Booster, Divi LearnDash Kit, etc) can be purchased with a single-site license. If you are wondering whether you can use the license on both a production site and a staging site at the same time, the answer is yes!

Once a license is activated on a site the details of the activation are stored in the database, with no further checks made to the license server. This means that if you copy the site then both the original and the copy should be activated and able to receive updates. So:

• If you copy from staging to production (i.e. staging is the "master" copy)… you'd need to activate the license on staging
• If you copy from production to staging, make changes in staging and then copy back to production (i.e. production is the "master" copy)… you can either activate the license on production before copying to staging, or alternatively activate it on staging before copying back to production

In either scenario the activation details will be propagated to both sites and both will be active. As long as you're always copying from an activated site there should be no further need to enter the license key.