Can't send Firebase Cloud Messages if function is called by Google Tasks

Question

I have an .onCreate cloud function, that once triggered, creates a task and runs it.

If I simply run admin.messaging().sendToDevice(payload.tokens, payload.message); inside the exports.createScheduledNotification function, then it runs fine, but I wanted to utilise Cloud Tasks so that I can schedule the task a little further into the future.

However, even if the entire payload is inside the scheduledNotification function, it still doesn't run. I have a feeling that it's actually not being called at all. However, I've checked in the Google Cloud Tasks console, and it shows that it has run, but I get no response from the Firebase Messaging at all, so from that I can deduce it's not running.

Is there something wrong with how I'm sending the task request? Is the cloud function that receives the call written incorrectly?

Cloud Functions & Tasks Set up and Imports 'use strict';

const functions = require('firebase-functions');
var admin = require("firebase-admin");

const { CloudTasksClient } = require('@google-cloud/tasks')

var serviceAccount = require("./secret_file.json");

admin.initializeApp({
  credential: admin.credential.cert(placeholder_for_account_credentials)
});

Function that is meant to create and send a Google Task, which is meant to call an .onRequest function, to send a Firebase Message

exports.createScheduledNotification = functions.firestore.document('/followers/{followedUid}')
.onCreate(async (snapshot) => {
    const data = snapshot.data();

    const tasksClient = new CloudTasksClient();
    const queuePath = tasksClient.queuePath(project, location, queue);

    const url = `https://{placeholder_for_location}-{placeholder_for_project_id}.cloudfunctions.net/scheduledNotification`;
    const docPath = snapshot.ref.path;

    const task = {
      httpRequest: {
        httpMethod: 'POST',
        url,
        body: Buffer.from(JSON.stringify({})).toString('base64'),
        headers: {
          'Content-Type': 'application/json',
        },
      },
      scheduleTime: {
        seconds: 10 + Date.now() / 1000
      }
  };
  
  try {
    await tasksClient.createTask({ parent: queuePath, task });
    
  } catch (error) {
    console.log(error);
  }
});

Function to accept a call from Google Tasks, and then sends a message to a selected device_id

exports.scheduledNotification = functions.https.onRequest((req, res) => {
    const payload = {
      message: {
        notification: {
          title: 'You have a new follower!',
          body: `Moe is now following you.`,
          sound: 'default'
        },
      },
      tokens: ["placeholder_for_device_id"]
    };

    admin.messaging().sendToDevice(payload.tokens, payload.message);
});

I would also like to mention that I saw in another question I needed to allow the principal firebase account to be able to create tasks, and I've added Cloud Task Admin and Cloud Task Enqeuer to every single account, and that the task are showing up in the Cloud Tasks Console.