Why does my Google Maps map say “For development purposes only” and/or is disabled?

• No API key stored in the plugin
  
• Means of payment in Google Cloud Platform expired/invalid (ClientBillingNotEnabledMapError) or (BillingNotEnabledMapError).
  
• The domain is not enabled for the API key stored in the plugin

Related links

• Google Maps API Key
• Google ExpiredKeyMapError
• Google Maps RefererNotAllowedMapError