curl --request POST \
  --url http://localhost:8080/miniapp/subscription/purchase/preview \
  --header 'Content-Type: application/json' \
  --data '
{
  "initData": "<string>",
  "subscriptionId": 123,
  "selection": {},
  "periodId": "<string>",
  "periodDays": 123,
  "period": "<string>",
  "trafficValue": 123,
  "traffic": 123,
  "trafficGb": 123,
  "servers": [
    "<string>"
  ],
  "countries": [
    "<string>"
  ],
  "serverUuids": [
    "<string>"
  ],
  "devices": 123,
  "deviceLimit": 123
}
'

{
  "success": true,
  "preview": {},
  "balanceKopeks": 123,
  "balanceLabel": "<string>"
}