curl --request POST \
  --url https://api.messaging.phonovation.com/sms/1/preview \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data @- <<EOF
{
  "text": "Let's see how many characters remain unused in this message."
}
EOF

{
  "originalText": "Let's see how many characters remain unused in this message.",
  "previews": [
    {
      "textPreview": "Let's see how many characters remain unused in this message.",
      "messageCount": 1,
      "charactersRemaining": 100,
      "configuration": {}
    }
  ]
}