Audio Files Stored in S3 are not Playable

I can successfully upload audiofiles to AWS S3, however the files do not play whether downloaded or played in the browser. The files do have a filesize.

I’m uploading an audioBlob object to AWS S3:

const [audioBlob, setAudioBlob] = useState(null)


const submitVoiceMemo = async () => {
    try {
      await fetch('/api/createVoiceMemo', {
        method: 'PUT',
        body: audioBlob
      })
    } catch (error) {
      console.error(error)
    }
  }

This is the API Route:

module.exports = requireAuth(async (req, res) => {
  try {
    AWS.config.update({
      accessKeyId: process.env.AWS_ACCESS_KEY_1,
      secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY_ID,
      region: 'us-east-2',
      signatureVersion: 'v4'
    })

    const s3 = new AWS.S3();

    const uuid = randomUUID()
    const s3Params = {
      Bucket: 'waveforms',
      Key: `voicememo/${uuid}.mp3`,
      Body: req.body,
      ContentType: 'audio/mpeg',
      ACL: 'public-read'
    }

    await s3.upload(s3Params).promise()

  } catch (e) {
    res.status(500).json({ error: e.message })
  }
})

As per this question, I have confirmed that req.body is a string.

The file being received by S3 has a filesize and the correct contentType when checked in the S3 console. It just isn’t playable when downloaded or played directly in the browser.

---

Below is how audioBlob and also audioFile (an MP3) are generated (Basically the user records a voice memo and when they click stopRecording, raw audio is stored as state):

const stopRecording = () => {
    recorder.current
      .stop()
      .getMp3()
      .then(([buffer, blob]) => {
        const file = new File(buffer, 'audio.mp3', {
          type: blob.type,
          lastModified: Date.now()
        })
        setAudioBlob(blob)
        const newBlobUrl = URL.createObjectURL(blob)
        setBlobUrl(newBlobUrl)
        setIsRecording(false)
        setAudioFile(file)
      })
      .catch(e => console.log(e))
  }

How can I correctly store audio generated on the front-end, in S3?