That error shows that you are using multiple google maps or it may be possible your default theme comes with a google maps functionality so both apis are conflict and creating issue.
If you are using multiple maps than you need to remove another maps api or theme google map api to resolve this issue. After disable another api your issue will be resolved.
I tried activating default Twenty Seventeen theme and issue didn't go anywhere.
Tried disabling all other plugins, leaving just map - doesnt work.
This is not a theme issue, please send us your wp login details at email@example.com so we can setup new api key for you and resolve your issue.
This question is now closed