# Sudden error message in /audio/merge robot

**URL:** <https://community.transloadit.com/t/sudden-error-message-in-audio-merge-robot/16858>\
**Category:** Transloadit\
**Created:** [October 20, 2023, 8:01am UTC](https://community.transloadit.com/t/sudden-error-message-in-audio-merge-robot/16858 "2023-10-20T08:01:19Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Gorgsenegger](https://avatars.discourse-cdn.com/v4/letter/g/a587f6/32.png) [@Gorgsenegger](https://community.transloadit.com/u/Gorgsenegger)\
**Post date:** [October 20, 2023, 8:01am UTC](https://community.transloadit.com/t/sudden-error-message-in-audio-merge-robot/16858/1 "2023-10-20T08:01:20Z")

</div>

I’ve been using the `/audio/merge` robot for almost a year now and didn’t have any problems (except initially setting my template up). Since yesterday I keep getting the error message

`Invalid audio stream. Exactly one MP3 audio stream is required.`

when trying to merge two mp3 files, the relevant part of the code is

```auto
    ...
    "merge": {
      "use": {
        "steps": [
          {
            "name": "concatenated",
            "as": "audio"
          },
          {
            "name": "normalized",
            "as": "audio"
          }
        ],
        "bundle_steps": true
      },
      "robot": "/audio/merge",
      "duration": "longest",
      "ffmpeg_stack": "v6.0.0",
      "sign_urls_for": 120
    },
    ...

```

The only recent change was updating the `ffmpeg_stack` version from `v4.3.1` to the [recommended](https://transloadit.com/docs/transcoding/audio-encoding/audio-presets/) version `v6.0.0`

---

<div class="post-metadata">

**Author:** ![Gorgsenegger](https://avatars.discourse-cdn.com/v4/letter/g/a587f6/32.png) [@Gorgsenegger](https://community.transloadit.com/u/Gorgsenegger)\
**Post date:** [November 3, 2023, 8:48am UTC](https://community.transloadit.com/t/sudden-error-message-in-audio-merge-robot/16858/2 "2023-11-03T08:48:51Z")

</div>

The problem is with version 6, choosing version 5 fixes it (for now).