Push Notifications on Android are sent with the help of the FCM service. To work with it, two keys are required: a client and server key. If you have a project, move on to the second part of this article.
Use resources of your app. For example, R.drawable.ic_launcherIcons which set in the push-notification wizard have priority over the icons which set in these methods.
In case you use several push notifications services or would like to use your own implementation of FirebaseMessagingService, please add the call of the method for displaying messages sent from the devtodev system: