curl --request POST \
  --url https://api.heygen.com/v3/assets \
  --header 'Content-Type: multipart/form-data' \
  --header 'x-api-key: <api-key>' \
  --form file='@example-file'

{
  "data": {
    "asset_id": "<string>",
    "url": "<string>",
    "mime_type": "<string>",
    "size_bytes": 123
  }
}