You need to create and enter a Google Maps Key code.
1. After setting up a Google developer's account, simply grab your key here.
2. In your WP-admin, navigate to the MapifyPro tab, and select "MapifyPro Settings". You'll see the field where you need to paste the code. It's as easy as that. Note however that you MUST update to the latest version of MapifyPro to see this new field. Here's a visual: