MapSVG needs 2 Google API keys:
Since summer 2018 Google requires providing billing details in order to use their API. There is a free quota of 28,000 Google Map views per month and 2,500 Geocoding API requests per day. You won't be charged if you don't exceed the limit.
Sign in to Google Cloud Console and provide your billing details.
Google Maps API and Geocoding API services will not work if you don't provide your card details to Google.
Select Application Restrictions > HTTP referrers\ and enter 2 URLs as follows:
If you did all steps above and Google Maps are not working in MapSVG or if you can't add markers - open Google Cloud console > Menu > API & Services > Library again. Turn off both APIs and enable them again.