sending push notif withe firebase function/cloud messaging

How to / Third Party Tooling
1

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 https://exp.host/--/api/v2/push/send

but I’m encountering these errors

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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')

admin.initializeApp(functions.config().firebase)

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

  return admin
    .database()
    .ref('users')
    .once('value')
    .then(snapshot => {
      snapshot.forEach(childSnapshot => {
        var expoToken = childSnapshot.val().expoToken

        if (expoToken) {
          messages.push({
            to: expoToken,
            body: 'Test Notification'
          })
        }
      })

      return Promise.all(messages)
    })
    .then(messages => {
      fetch('https://exp.host/--/api/v2/push/send', {
        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.