On application launch, app starts the service that should to do some network task. After targeting API level 26, my application fails to start service on Android 8.0 on back
Yeah, that's because you can't start services in the background anymore on API 26. So you can start ForegroundService above API 26.
You'll have to use
ContextCompat.startForegroundService(...)
and post a notification while processing the leak.