The first thing you’ll need to do is get credentials to use Google's API. 

I’m assuming that you’ve already created a Google account and are signed in. 

Head over to Google API console and click "Select a project" in the header. 

 

Create a new project if you don’t have any project 

 

Next, Enter Your Project Name and Click on Create

 

Next up we must specify which APIs the project may consume. From the header, select "Enable APIs and Services".

 

On the next page, search for "Maps" and Enabled following API from the list.



Next Switch to APIs & Services 

 

Now go on Credentials 


Now press “Create Credentials” 


 

Select API key

Now you get “API key”

Note: Restrict the API key of your application for security.


In Admin Dashboard you need to enter the API key in Google Map Key.


Now application ready for Google Map


Note: If you get a Message on Map For Development purposes only then you didn't enable billing on the project please enable billing on the project to remove that message. Also, all Map functions do not work properly.


For more information please read this 

https://developers.google.com/maps/documentation/javascript/error-messages?utm_source=places_js&utm_medium=degraded&utm_campaign=keyless#api-key-and-billing-errors