2018-02-20T21:16:49.878Z E receiveMessage: TypeError: admin.messaging(...).send is not a function
at exports.receiveMessage.functions.database.ref.onCreate (/user_code/index.js:55:27)
at Object.<anonymous> (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:59:27)
at next (native)
at /user_code/node_modules/firebase-functions/lib/cloud-functions.js:28:71
at __awaiter (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:24:12)
at cloudFunction (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:53:36)
at /var/tmp/worker/worker.js:695:26
at process._tickDomainCallback (internal/process/next_tick.js:135:7)

const functions = require('firebase-functions');

const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

// // Create and Deploy Your First Cloud Functions
// // https://firebase.google.com/docs/functions/write-firebase-functions
//
// exports.helloWorld = functions.https.onRequest((request, response) => {
//  response.send("Hello from Firebase!");
// });
exports.recceiveInvitation = /* the function that works */;

exports.receiveMessage = functions.database.ref('/messages/{chatId}/{time}').onCreate((event) => {
    const chatId = event.params.chatId;
    console.log('messages', chatId);
    var sender = event.data.val().name;
    var messageContent = event.data.val().message;
    if(messageContent.length >= 100){
        messageContent = messageContent.substring(0,97)+"...";
    }
    const payload = {
        data: {
            title: `New Message from ${sender}`,
            body: messageContent
        },
        topic: chatId
    };

    return admin.messaging().send(payload);
});