curl --request POST \
  --url https://api.beltic.com/v1/identity/documents/idvs/{id}/files \
  --header 'Content-Type: application/json' \
  --header 'X-Api-Key: <api-key>' \
  --data '
{
  "data": {
    "type": "file",
    "attributes": {
      "filename": "<string>"
    }
  }
}
'

{
  "data": {
    "type": "file",
    "id": "123e4567-e89b-12d3-a456-426614174000",
    "attributes": {
      "id": "<string>",
      "filename": "<string>",
      "url": "https://s3.amazonaws.com/...?X-Amz-Signature=...",
      "content_type": "<string>",
      "byte_size": 123,
      "checksum": "<string>"
    }
  },
  "meta": {
    "presigned_upload_url": "https://s3.amazonaws.com/beltic-documents/...",
    "expires_in": 3600
  }
}