I refer to a answer given by Mike20132013 on This IP, site or mobile application is not authorized to use this API key.
Mike in point 5 you say: Once you are done, click create and your new Server Key will be generated and you can then add that server key to your URL.
Sorry, I am lost here. I have created a server key but to which URL are you referring to? Where exactly do I enter this URL please? I have bought the Google Reviews Plugin and I get the error message "REQUEST_DENIED: This IP, site or mobile application is not authorized to use this API key. Request received from IP address 46.249.199.28, with empty referer" on my website. My host has referred me to your answer.
Then you say
"Last thing is that, instead of putting the sensor=true in the middle of the URL, you can add it in the end like this:
I have no idea where to input this.