I created this small code to reproduce the error I was getting inside an app:

const async = require("async");

function sleep(ms) {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

const parallels = [];

for (let i = 0; i < 2; i++) {
  parallels.push(async function (callback) {
    const randomSleepTime = Math.ceil(Math.random() * 10000);
    await sleep(randomSleepTime);
    callback(randomSleepTime);
  });
}

async.parallel(parallels, function (err, results) {
  console.log(err);
  console.log(results);
});

I'm getting this error after this is done: TypeError: callback is not a function
Why exactly is this happening?