Sending push notifications to Android devices is done via Firebase Cloud Messaging. You'll need to generate a .JSON server key, which you enter in the push notification settings. Steps are given below.
Make sure that the Firebase Cloud Messaging API is enabled for your project. You can check that here.
Log into the Firebase Console for your project
Head into your Project settings by clicking on the gear icon in the sidebar:
Select the Service Accounts tab and click on the Generate New Private Key button. You will see a confirmation dialog after which the prompt to download the credential file should appear
Login to Growlytics Dashboard.
Go to Integrations => Mobile Push Notifications.
Upload FCM credentials file.
Add the Android notification channels you are using, make sure the channels you are mentioning here is registered in your app, you will not get notifications otherwise. Channel is mandatory to send notifications.
Click on "Submit Credentails" Button. When clicked, you will be asked to test those credentials.
Enter title and message body for sending test notification.
Enter FCM Token of the device to whom you want to send test notification.
Select any notification channel which you've provided earlier.
Click on "Send Test Notification & Save Credentials" Button.