Google maps not displayed (key problem)

Hi and thanks for this great plugin,
I have problems when I activate the google map option.
It starts to display the map then displays an error
By looking at the JS debug console,I have the following message:
“Google Maps API error: MissingKeyMapError https://developers.google.com/maps/documentation/javascript/error-messages#missing-key-map-error”
Any idea?
Thanks!!