Hi, I signed up, paid for credit, created & added the google API key (see below if it was done correctly), and installed the wordpress plugin.. to test it, I used a plagiarized article, which shows 100% unique content. I've included screenshots, so you can see both the plagiarized text and results.
The documentation in the plugin on generating the Google API key is not current, but what I did was create an API credential in https://console.developers.google.com like so (xxx for privacy):
Key for browser applications
Mar 4, 2014 3:01 PM
and entered the API key in my http://proofreadbot.com/ account (there is no error check, so wanted to include this, in case it is the problem)
Please advise - Ari