Once you buy our premium/plus theme you will get license in your email along with the .zip file. The license is needed for us to give you better support. You can use the license in mutliple WordPress websites of yours.
Check your email for the license.
Once you install and activate the premium/plus theme, you will be asked to enter your license in the dialogue box below.

You can simply enter the license number and click “Agree & Activate License”