Ruby bindings to Firebase Cloud Messaging (FCM) for Android, iOS or Web

For your server to send a message to one or more devices, you must first initialise a new FCM class with your Firebase Cloud Messaging server key, and then call the send method on this and give it 1 or more (up to 1000) registration tokens as an array of strings. You can also optionally send further HTTP message parameters like data or time_to_live etc. as a hash via the second optional argument to send.