just tried with your code on my server and my api key and it’s working fine.
A couple questions. Are you using a child theme?
On google’s site it says:
If you are loading Maps JavaScript API from the deprecated v2 path, you will get the NoApiKeys warning, even if you specified the key parameter. Please check the v2 to v3 upgrade guide and migrate your application to Maps JavaScript API v3.
Maybe try a new API key?
