Error when uploading worker script via API

Hello, been trying to upload a worker module via the Cloudflare API, but I'm running into the following error message:

{
  "code": 10021,
  "message": "Uncaught TypeError: Main module name is not present in bundle.\n"
}

{
  "code": 10021,
  "message": "Uncaught TypeError: Main module name is not present in bundle.\n"
}

{
  "code": 10021,
  "message": "Uncaught TypeError: Main module name is not present in bundle.\n"
}

{
  "code": 10021,
  "message": "Uncaught TypeError: Main module name is not present in bundle.\n"
}

I've tried testing with the exact code from the API docs (https://developers.cloudflare.com/api/operations/worker-script-put-content) via javascript and curl, but both generate the same issue. I can upload workers in service worker format fine.

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