Google requires you to register an API key so that you can show Maps on the site. Please follow these steps to get the key:
Step 1: Login to your Google account and Go to this link https://console.developers.google.com
Step 2: Agree with Terms of Service if this is the first time you have gone to this link.
Besides, go to Google APIs , search for Google Place API Web Service and click Enable
Step 4: Select an existed project or Create new, then click Continue.
♣ Choose HTTP referrers (websites) in Key restriction section
♣ Fill in your domain. You can use multiple domains, but one should match the current domain. For example, link of your site is https://www.jobmonster.com, you will enter *.jobmonster.com/*
Step 6: Click Create.
Step 7: Copy the API Key then paste into the setting above.
For more reference, you can see: Official Document, Google Blog