Question: How to create API key in Google Console
Answer: Make sure to follow the steps at
https://developers.google.com/codelabs/setup-perspective-api At the moment Google requires to contact them to enable the API.
After that visiting Credentials page of your project and choose to create Credentials of type API Key -
http://prntscr.com/kw3yl9 and set the key created in the add-on settings. The API key resitrictions should whitelist your server IP and whitelist the API it gets access to.