OneSignal

Having OneSignal in your app will have two features: 1-Drivers will get notification even when app is in background. 2-You can send manual push notifications to drivers or riders containing promotional messages.

Setup OneSignal

You have already created two OneSignal apps. Now you will need to Only get the Server Key & Sender Id of your applications from their firebase console's project settings under Cloud Messaging Section and put them in Android setup of your OneSignal project. Then put their Application Ids under their corresponding section in your build.gradle of driver & rider.