curl --request POST \
  --url https://converso-whatsapp-api.p.rapidapi.com/chat/getBase64FromMediaMessage/{instance} \
  --header 'Content-Type: application/json' \
  --header 'instanceCode: <api-key>' \
  --header 'x-rapidapi-key: <api-key>' \
  --data '
{
  "message": {
    "key": {
      "id": "<string>"
    }
  },
  "convertToMp4": true
}
'

This response has no body data.