curl --request POST \
  --url https://api.{your-broker}.slate-labs.com/email-templates/{template_id}/preview \
  --header 'Content-Type: application/json' \
  --data '
{
  "locale": "en",
  "sample_data": {}
}
'

{
  "detail": [
    {
      "loc": [
        "<string>"
      ],
      "msg": "<string>",
      "type": "<string>"
    }
  ]
}