sending push notif withe firebase function/cloud messaging

Hi, I’m using firebase function and cloud messaging to send notifications.

the way it works is when a webhook pushed an entry to real time database the function will be called to send push notifs to all users using expo

but I’m encountering these errors

It says on the pricing plan that cloud messaging and function is free but why am I experiencing this error? I’m on Spark plan

this is how I send or handle the function

var fetch = require('node-fetch')
const functions = require('firebase-functions')
const admin = require('firebase-admin')


exports.sendPushNotifications = functions.database.ref('new_content_store/{id}').onCreate(() => {
  var messages = []

  return admin
    .then(snapshot => {
      snapshot.forEach(childSnapshot => {
        var expoToken = childSnapshot.val().expoToken

        if (expoToken) {
            to: expoToken,
            body: 'Test Notification'

      return Promise.all(messages)
    .then(messages => {
      fetch('', {
        method: 'POST',
        headers: {
          Accept: 'application/json',
          'Content-Type': 'application/json'
        body: JSON.stringify(messages)

I’ve done a research too, but most of the answers/problems are dated back 2017 with the old firebase plan. And there is also a similar question to mine here but got no answers.