Firebase android misses important feature of android notification like `group`, `priority` and etc. As a work around you can send data message (no `notification` payload at all) and this repo will build a local notification for you. If you pass `custom_notification` in the payload, the repo will treat the content as a local notification config and shows immediately.
NOTE: By using this work around, you will have to send different types of payload for iOS and Android devices because custom_notification isn't supported on iOS
