I purchased the app through Google Play Store but didn’t receive an activation key to unlock it.
There is NO license key for purchases on the Google Play Store.
nIt works fully automatically with your Google account. You should see that the purchased version or feature is unlocked. If not, please restart your device and recheck it.
If you have a MY.PROTECTSTAR user account, you do not see a license or an edition listed there for purchases you made on the Play Store.