curl --request POST \
  --url https://api.example.com/cabinet/subscription/tariff/switch/preview \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "tariff_id": 123,
  "period_days": 1825,
  "traffic_gb": 50000
}
'

{}