Google maps API now requires a key, read more about the changes here.
Regarding the process of getting a key, follow these steps:
- Head to Google developers console and login.
- Now you’ll need to create a new project, you can do that here.
- At the left side menu click Credentials and create a credential for Api key > Browser key
- After clicking the create button you’ll see your API key, this is the key you need to use!