How to install the Plesk license?
To install the Plesk license, use your activation code - a combination of numbers and letters XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXXXXX.
Go to Tools & Settings > License Information (License Management in previous Plesk versions) > click Install Key.
Note: To install an additional purchased license, click the Retrieve Keys button. If the purchased license was not retrieved, switch to the Additional License Keys tab and click the Install key button to install it manually.
Enter your Plesk activation code and click OK.