title: How to send push notification to specific devices
body: <p>I got two mobile apps for service provider and customer, i need to send push notifications for service provider user once the customer requests a specific service type. So it needs to be filtered and send only for those who can provide such a service. Therefore web api needs to send the notification only for specific users, how can i do that with <code>firebase</code> should i use, <code>device mac</code> or <code>registration id</code> generated by <code>firebase</code>.</p>
  
  <p>Any help</p>