Google Map API key is required to make this plugin work. So you need to generate api key and put this api key in WP Ride Booking plugin settings. To generate an api key you need to follow below steps :
1. Go to cloud console and create project for which you want to add an api key.
2. Go to APIs & Services > Credentials page.
3. On Credentials page, choose project and then click Create Credentials > API key page.
The dialog displays your newly created api key.