curl --request POST \
  --url https://api.unibee.dev/merchant/plan/active_price_change/preview \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "newAmount": 123,
  "planId": 123
}
'

{
  "code": 123,
  "data": {
    "activeAffectedSubscriptions": 123,
    "newAmount": 123,
    "oldAmount": 123,
    "planId": 123,
    "totalAffectedSubscriptions": 123
  },
  "merchantId": 123,
  "message": "<string>",
  "redirect": "<string>",
  "requestId": "<string>"
}