curl --request POST \
  --url https://api.example.com/v1/voiceai/knowledge-base/files \
  --header 'Content-Type: multipart/form-data' \
  --header 'x-api-key: <api-key>' \
  --form 'files=<string>' \
  --form files.items='@example-file'

{
  "success": [
    {
      "id": "<string>",
      "name": "<string>",
      "size_bytes": 123,
      "type": "file"
    }
  ],
  "failed": [
    {}
  ]
}