Sign in to the Google account tied to your app’s Firebase project. Then follow this link.
Click the project your app is set up on to select it.
On the left menu, under Engage, click Messaging.
On the top-right corner, click New Campaign. A small pop-up will appear, click Notifications.
Input the values needed under Notification, then click Next.
Now under Target, click Select an app and choose the app(s) you want to send the notifications to.
To send to multiple apps, click Target another app. To delete an already selected app, click the bin icon at the end of the already-added targeted app
Under scheduling, select if you want to send the notification now, or at a later date and time.
For Conversion events (optional), you can set what you want to be reported in your Google Analytics dashboard when an action is taken on your notification(s). If you know what to do here, go ahead, else, skip by clicking next.
Additional options (optional) are for any other options. You can set Android Notification Channel for more Channel options, Custom data for custom information you want sent with the notification, and Sound for ensuring your notification delivers with a sound. Now here you can also set how long you want the notification to stay on the user’s device before it automatically clears away if the user does not take action on the notification bubble on their device. This can be done under Expires.
When you are done, you can either save as draft and complete it later for sending or Send it immediately with Review.
When you click review, a review dialog box appears showing you a summary of your push notification settings. When ready, click Publish.
Please note, that the delivery of push notifications might be delayed sometimes due to server speed, network, and service availability. So if the notification is not delivered immediately, it might be delivered at a later time. You just have to be patient with it sometimes.