What is a Device token?

Question:

What is a Device token? 

Answer:

Push token (device token) - is a unique key for the app-device combination which is issued by the Apple or Google push notification gateways. It allows gateways and push notification providers to route messages and ensure the notification is delivered only to the unique app-device combination for which it is intended.

iOS device push tokens are strings with 64 hexadecimal symbols. Push token example:
03df25c845d460bcdad7802d2vf6fc1dfde97283bf75cc993eb6dca835ea2e2f
Make sure that iOS push tokens you use when targeting specific devices in your API requests are in lower case.

Android device push tokens can differ in length (usually below 255 characters), and usually start with APA91b…, however it might also have a colon-separated prefix. Push token example:

APA91bFoi3lMMre9G3XzR1LrF4ZT82_15MsMdEICogXSLB8-MrdkRuRQFwNI5u8Dh0cI90ABD3BOKnxkEla8cGdisbDHl5cVIkZah5QUhSAxzx4Roa7b4xy9tvx9iNSYw-eXBYYd8k1XKf8Q_Qq1X9-x-U-Y79vdPq

Using raw device tokens for targeting specific devices is not the most reliable way because FCM push tokens tend to change from time to time, and it’s hard to tell how often it occurs.