Q: I get an error about license failure something even though I purchased the plugin. What should I do?

The bug is on the Google Licensing Server or in Google Play App that for some strange reason randomly causes a data corruption in the settings and refuse the connection to the App. 

A workaround is this:
1) Unistall the app
2) Clean all Google Play Store App data not only the cache, and Google Play Service data, in the phone setting. (this will reset all settings to default in both these apps)
3) Reopen Google Play and accept the end-user license agreement.
4) Reinstall the app.