If the message "This page can''t load Google Maps correctly." and/or “for development purposes only” is displayed, this can be for the following reasons:

• No API key was provided
• Billing has not been enabled on Google account linked to the API.
• The provided billing method is invalid (for example an expired credit card).
• A self-imposed daily limit has been exceeded.

More information can be found on the Google Maps API documentation website.