curl --request GET \
  --url https://api.penciled.com/v1/variables \
  --header 'Authorization: Bearer <token>'

{
  "variables": [
    {
      "variable": "patient_first_name",
      "type": "patient_first_name"
    },
    {
      "variable": "patient_phone_number",
      "type": "patient_phone_number"
    },
    {
      "variable": "appointment_dates",
      "type": "date[]"
    },
    {
      "variable": "callback_number",
      "type": "phone_number"
    }
  ]
}