Refund a card payment

curl --request POST \
  --url https://api.suby.fi/api/refund/{paymentId} \
  --header 'Content-Type: application/json' \
  --header 'X-Suby-Api-Key: <api-key>' \
  --data '
{
  "reason": "Customer requested refund"
}
'

{
  "success": true,
  "data": {
    "paymentId": "pay_abc123",
    "status": "REFUNDED"
  }
}