What is FCM device token?

Firebase Cloud Messaging (FCM) is a messaging solution that lets you reliably send messages at no cost to both Android & iOS devices . Using FCM, you can send data payloads (via a message) to a device for a specific application. Each message can transfer a payload of up to 4KB to a client.

It’s my first time using FCM. I download a sample from firebase/quickstart-android and I install the FCM Quickstart.

Configure Web Credentials with FCM