You get these errors if you enter a license you purchased from Balsamiq in the app's licensing box provided by Atlassian's Universal Plugin Manager.
That text area only accepts Atlassian Marketplace-generated licenses. To enter your Balsamiq-generated license information, click on Configure, and you'll see this screen:
Click on "Balsamiq", and you'll see this screen:
Enter your license name and key there, and it will work.
Once you have successfully registered your Balsamiq-generated license, the Atlassian registration screen will still show your app as "Unlicensed."
Heads up: If you have a Marketplace trial license installed, you might not see a Configure button at all. Delete your Marketplace license key and hit update to make the Configure button re-appear. This will allow you to enter a Balsamiq-issued license instead.