title: Send notification from the server to user segment who installed the app
body: <p>In Firebase console, I saw the option to send a notification to User Segement with app "com.example" (where com.example is the app name).</p>
  
  <p>As the image shows:</p>
  
  <p><a href="https://i.stack.imgur.com/cke4t.png" rel="noreferrer"><img src="https://i.stack.imgur.com/cke4t.png" alt="enter image description here"></a></p>
  
  <p>But how to do it from the server side using the FCM REST API:</p>
  
  <p><a href="https://fcm.googleapis.com/fcm/send" rel="noreferrer">https://fcm.googleapis.com/fcm/send</a></p>