curl -X POST "https://olive-gateway-a6ba.onrender.com/api/v1/wallet/balance/sub_abc123" \
  -H "Authorization: Bearer olive_live_xxx" \
  -H "Content-Type: application/json" \
  -d '{
    "pin": "1234"
  }'

{
  "success": true,
  "balance": 12500000,
  "balance_formatted": "125,000.00 SLE",
  "currency": "SLE",
  "subscriber_id": "sub_abc123",
  "last_transaction_at": "2025-01-15T10:30:00Z"
}