These instructions will help you unlock your Google Sheets add-on with your activation key. Please follow the steps below (by example of Power Tools) to activate your subscription.
Go to Extensions > Power Tools > Start:
Click on the key icon at the bottom of the add-on sidebar. Copy and paste your key from the registration email into a special field in the tool and click Activate my subscription:
As soon as the subscription is activated, you will see all the related info in one place upon clicking the same key icon at the bottom of the add-on window: