Receiving device_token with google cloud messaging?

Good afternoon.
Want to unsubscribe from the push service of rassylok gravitec.
Used to use a bunch of google cloud messaging + gravitec. In fact all the customers who signed up remained in the GCM.
The question is, how do I do rassylku in php, since I don't know the device token. All the data that gave polzovatelei subscriptions are stored at gravitec.
Or maybe there is a way to get these tokens from the GCM.
Searched through the documentation, found nothing. But how to send a push with a key.
March 19th 20 at 09:03
1 answer
March 19th 20 at 09:05
Notification subscription
https://habr.com/ru/post/321924/
<html>
the <head>
 <meta charset="utf-8">
 <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

<script
src="https://code.jquery.com/jquery-1.12.4.min.js"></script>
</head>
the <body>
<button type="button" id="subscribe">Monitor changes</button>
</body>
</html>
<script src="https://www.gstatic.com/firebasejs/5.4.1/firebase.js"></script>
<script type="text/javascript" src="/firebase_subscribe.js"></script>

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